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Integrating member selection and structural appraisal in the design of steelwork
Integrating member selection and structural appraisal in the design of steelwork P Toms and J O Surtees * The paper describes a prototype computer aid for the design o f steelwork based on a reappraisal o f the handling of design information. Interactive computer assistance derived essentially from manual design procedures is examined and the relationship between designer and computer discussed. Characteristics o f the design process are considered and the design check defined, being the basic source o f information for design decisions. The computer aM operates as an executive system for handling design checks hem in a library. Relevant checks are carried out sequentially for all structural parts without concurrent display of results. Compact displays of design information available at the end o f this process facilitate assessment and reselection o f material. The technique for displaying details o f all checks carried out, including internal logic, parameters and performance indicators is described and illustrated. computer aid, design chech, computer-designer relationship
Microcomputer programs available to assist the design of specific classes of building structure are generally based on the manual design process. That is, critical design factors are considered in a sequence known from experience to be expeditious for designing the type of structure in question. Design calculations are handled in separate modules which reflect traditional code of practice design of elements. Hand calculation methods are mechanized and the user is simply required to supply data at predetermined points in a conventional design sequence. It is argued 1 that this method simplifies both program operation and checking of resuIts. Computer-aided design of steelwork structures is usually based on this approach Programs for the design of portal frames 2'3 commonly use a design procedure4 proposed for manual design. To improve a design, some programs allow certain data to be modified and rerun. Such design changes must draw inspiration from the limited information displayed during program runs. Thus in Yeadon 2, a design program module determines a collapse mechanism for the frame and carries out an initial selection of members, essentially following the procedure described by Morris and Randell 4 . Using other modules, the designer may opt to check rafter, haunch and stanchion stability and thus determine the position of necessary lateral restraints. Further self-contained programs may be used to check deflection and design elements such as purlins and rails. In Laxon et al 3 design selection is carried out to preset Structural Design Information Software, Leeds, U K
*Department of Civil Engineering,University of Leeds,Leeds,UK
volume 17 number :2 march 1985
criteria, without interaction. Design feedback is restricted to lists of quantities and costs, with optional listing of formal design calculations as design proceeds. In an approach, based primarily on preconceived solutions, the relationship of designer to computer is supplementary. A style of interaction limited essentially to response to prompts for information has been evolved. A program developed according to this approach for the design of structural elements s characterizes control of the computer by the use of the command GO and the role of the user by the command HELP. When the computer halts at some stage of a predetermined design process it waits for a command to proceed and offers prompts to help the user. This simple style of interaction is widely used in computeraided structural design. As a basis for interactive design, the above method of operation has shortcomings. Clearly, the designer should be in control of design strategy and the style of data presentation and commands should reinforce this. The form of presentation, based on routine output of information for each element as calculations proceed, is incompatible with this need as it makes spontaneous scrutiny of information at any of the design stages impossible. Results of protracted and repetitive calculations cannot be compared easily on scrolled screen display or paper listings. Limited ability to interact and access the current state of variables and the imposition of specific forms of design solution inhibit innovative design. Ideally, the computer should present information in a form most suited to assist design decision-making without undue delay from data processing activity. To enable changes in design strategy to be made, screen displays should allow design options to be readily identified. This requires procedures for handling and presenting design data which are different from those suited to achievement of preconceived designs or production of formal design documents. To this end, graphical computer display alongside textual presentation of values of certain design variables has been used by Moore and Brotton 6. Using informative interaction, their program simplifies the design of skewed steel beam-to-column connections, particularly in ensuring geometric compatibility of parts. It is clear that computerized design tasks should not dictate design strategy. There are few logical paths in conceptual design and it is important that the designer be allowed to explore novel arrangements. To this end, routine derivation of data must be combined with a facility to collate useful and perhaps unique sets of data for scrutiny. Programs based essentially on manual design procedures cannot be readily adapted to present the extensive design
0010-4485/85/0:20083-I I $03.00 © 1985 Butterworth & Co (Publishers) Ltd
83
information that would aid innovative design. This paper describes a method of computer assistance that extends the scope of information available for scrutiny during design. A program has been developed to ascertain the extent of interaction delays, ease of operation and influence on the design process. The prototype program addresses itself to steel framework design, though the principles adopted may be applied to structures incorporating other materials. It was conceived and written in anticipation of the powerful, low-cost microcomputers now available. The program aims to provide a total review of the performance of a selected structural arrangement, with convenient interactive facilities for carrying out a wide variety of design tasks. To do this, design checks are handled in a manner that is qualitatively different from manual design methods. Techniques adopted for the generation and presentation of information are based on a preliminary classification of data handled during design checking, as outlined below.
Outline configuration
STANDARD Specification scope Definition of part
Definition of parameters
Definition of mes~Jre of beheviour
Definition of performance
CHARACTERISTICS OF THE DESIGN PROCESS Two key activities in design are selecting material layout and checking that all relevant standards (including those concerning function and cost) are satisfied. Occasionally the two activities may be combined using routine procedures based on experience of handling critical design factors. Thus, steel section sizes may be selected considering a minimum collapse load factor only. However, further modifications are usually necessary when designing portions of the structure excluded from the routine procedure. For example, additional forces may arise from incidental bracing. Final review of the complete design is invariably necessary because routine procedures consider only a selection of relevant performance critiera. The assessment of the performance of a structural arrangement comprises two basic steps: •
identification of a basically similar arrangement which has been dealt with before • assessmentof aspects of its behaviour using convenient formulae to interpolate between available test data Overall, this can be called a design check. Access to information and design procedures from tests or previous applications is basic to this process. The scope of such information inevitably extends beyond that available in standard specifications and codes of practice. A designer will be aware of the following inherent limitations of design checks: • a standard check is applicable only to a limited range of configurations and material types • the required degree of precision necessary for parameters used in checks is not always readily understood • analysis routines invariably involve simplifications • alternative checks are often available for assessing performance and may yield different results To assist design decision-making, key features of a check should ideally be available for scrutiny along with results to enable the full implications to be appreciated. Figure 1 shows the activities and data flows involved in a structural design check. In practice, when performance is satisfactory, differences between the model contained in the standard and the proposed design configuration are often disregarded. The overriding objective in carrying out a check is to make easy further decision and action. Only a limited
84
Obtain relevant standard Propo~d confi~ration
Model configuration to standard
Modelled configuration Definition of material type, size and service conditions
Calculate data required for check
Calculated data required for check
Analyse model for behaviour in service
Performance indicators
Compute performance indicators
Judge performance and validity of model"
+ -- n~.. m C~ iLv )
informs activity store data source of data sequence of activities
Figure 1. Activities and information involved in a design check proportion of the total range of structural design checks is applicable to a given design. Within this limited proportion, only a small number of checks are likely to be critical. The effectiveness of a design check depends on its convenience with regard to data handling and also on a clear definition of the model incorporated and its reliability when correctly applied. Accuracy of results is not necessarily crucial.
Selecting a structural arrangement Design procedures evolve through accumulated experience of application. Short cuts are frequently used in the manual design process when checks known to be noncritical for the structure may be omitted. For example, certain design criteria are formulated in Morris and Randell4 for typical steel portal frame structures under load. Codes of practice and design guides permit routine selection of certain performance and manufacturing standards once element detail has been decided. At any point in design, choice of action is restricted to a small proportion of all the design tasks which must be undertaken in the course of the design. To determine possible courses of action requires access to and a review of relevant tasks and design information created so far in the design. Design can start with any selected configuration and does not follow a predetermined path. Initially, in the selection process, a comparison is made between present and previous design configurations, using performance data from design checks. The degree of comparison depends on the complexity of the design checks. Substitution of one part or more is then made and a new comparison carried out. Indicators of structural performance, together with cost, are used as the basisfor assessingthe merits of an innovation
computer-aided design
in design. An indicator might be scalar (for example, the proportion of working to permitted deflection at a point in a structure) or might simply show success or failure (the outcome of a design check). Judgement on whether standards are met requires consideration of all relevant indicators. To improve the performance of a scheme, a designer modifies the structure, selecting from the range of material available. The overall effect of alterations on the performance of the structure may not be apparent without considering all available data in combination. In practice the extent of this picture depends on the checks actually selected by the designer. It is clearly advantageous to have a total picture of the current scheme to assist further selection of material.
FUNDAMENTAL FEATURES OF A COMPUTER DESIGN AID Ideally, decision-making in design requires ready access to results of design checks carried out for a previous trial. However, results generated from a large number of design checks cannot be displayed simultaneously on a visual display screen. In practice, appropriate combinations of information need to be readily available for perusal. But, simply displaying results as calculations proceed severely limits useful juxtapositioning of data, unless calculations are repeated. In fact, display of results as calculations proceed is not necessary provided that all checks can be carried out rapidly and key results stored for attention later. To handle and present results of design checks in this way requires both an efficient data storage/retrieval system and new arrangements for communication of design information. A prototype computer program has been developed to assessthe handling of design checks by such means. The objective of the program was to assist the selection of member and haunch elements of a portal frame. Appropriate design checks from various sources, including the Draft BS 59507 (the scheduled replacement to BS 449) have been incorporated. Data used for checks is stored and retrieved by the computer in the categories summarized in Figure 1. Design checks are handled by the computer in a manner that provides a total review of performance. Selection and assessment of design checks are integrated in one computer aid through the adoption of the following technique for handling design information. After the data description of a structure has been input, design checks held in the program library can be selected and carried out automatically without display of results. The type of structure defined in the input specification determines which checks are required. To determine particular application of checks relating to the whole or part of the structure appropriate analyses are carried out and systematically inspected. All members and parts are checked sequentially and resulting design parameter values retained for optional viewing later. In addition, checks on behaviour of the structure as a whole are carried out. Rules of thumb or 'design insight' for identifying checks applicable to a particular type of structure are not used. For example, maximum shear in a simply supported beam is found through a search of analysis results, not by using a knowledge of its likely location. To incorporate the latter in a program would require either a previous declaration of element type or an automatic analysis to determine that it was a simply supported beam. The program may be regarded as a convenient operating
volume 1 ? number 2 march 1985
system for computerized design tasks. Its modular basis facilitates extension to cover many checks, including cost, for a variety of types of part. Control of subroutines .for parameter evaluation, design checks, display of results and filing of data is structured to allow easy insertion of further design features. Interactive commands for the scrutiny of design options and data are handled by a separate set of routines. A database representing full details of the design, both in terms of structural arrangement and performance, has been devised to exploit the method adopted for handling design checks. After constructing the database to accommodate detailed methods of data input and scrutiny of results for design decision-making, concise methods of handling data were added. Further methods and refinements can be developed using the adopted database. The program is fully operational, with error trapping and recovery procedures. It requires an interactive facility providing fast computing response and rapid access to stored data and was developed using a VAX 11/780 computer. However, the modular structure adopted was conceived to suit microcomputer operating systems.
DESIGN FACILITIES PROVIDED BY THE PROGRAM For convenient accessto a range of facilities that handle design checks for a complete structure, an executive system of program control is used. Control is passed back and forth along a tree of linked options, allowing design to proceed quickly by repeated modification and appraisal. Standard design tasks may be carried out in particular design situations at the will of the designer. This includes such tasks as changing the configuration of parts in a structure and display of full cost estimates. On command, all relevant checks held in the library of routines are carried out for the complete structure. Although this is the longest operation undertaken by the program, the delay is well within acceptable limits for interactive operation. For example, all checks for a threebay portal frame with haunches are carried out in about ten seconds. After this global operation, the designer may select displays of design information. Access to the results of checks is virtually instantaneous. To ease selection for the designer, a set of basic options for carrying out checks, displaying results, filing etc is provided as follows: • display structure and loading details • select and carry out relevant checks from the program library • display results oi~design checks • input or revise the description of the structure and loading details • display schedule and cost of available material • display concise definition of a nominated check or procedure • select and display definition of a specific parameter used in a check • file results of design checks for listing later or for the record After selection of a particular main option a set of secondary options may be displayed for the convenience of the designer. The tree of available options i~, shown in Figure 2. Access to some main options is provided at several points in the tree where appropriate.
85
tructural type atum details lear spaces nd restraints ~r-~ Material /~ [Details / I Load description / tDisplay data Start here Task control:
/
/
/
/
FEnter in detail ~ ..~ Derive using routine g e n e r a t i o n ~ L a y o u t and loads for portal frame truss I Obtain from f i l e ~ L.Member sizes I Revise data
Input data ---/ Display data ~ Carry out checks ~ Display check results----~ File output for printing \ File data,for p r i n t i n g \ Display information 7 \ Stop / \
/ / / / /
r-Mem r
-
~-
~
'FStructure and datum ] End restraint and material Details ~ L o I Load description [_Properties of parts
]End restraint "",----I Datum I Geometry a d s description l_Display data
FCheckscarried out [Check failures ~ Cost and ;p~rf~rmance of parts [Selected check results \ I Analyses \\ [_Estimated costs \ \ \ \ \ \ \ \ [List of available checks \ \
o''o
Z--- I Parameters---..___~List of definitions L_Material~ L_Derivation
"~-...__[-Types and forms I_Sizes available
[Overall I Compafibifi~y l Integrity [Functional performance l_Selected check results F 1 : Frames 2: Frame-bay /-1 3: Members 4: Member-portion / L_5:Member'section
\ Vc:::m : vau0, \
LCheckscarried out
~ ]-'Stability ~ _ ~ ~Defiection L_Costs
forces at nodes forces in members displacement of modes Weights of members
Figure 2. The tree o f design options contained in the program. Control may be passed back and forth between lists as indicated
To achieve rapid selection of an option, selection is made using a single digit code, as shown in the examples of screen output. The lists of options and codes may be suppressed if desired. On completion of a particular option, control is usually returned to the current list in use and the program pauses. Another option may then be chosen or the series redisplayed. A single keystroke returns control to the previous series. In practice, digital commands are assimilated quickly with experience and the program may be used without displaying options. As already mentioned, it is not possible to present all the design information from the global checking operation in one static display. Therefore the description of the structure and loading details, together with results of checks carried out have been broken down into convenient displays which the designer may peruse at will. The form and content of display strictly relate to the needs of structural design and are not merely a dump of data from memory, Data input and communication of results are described below and illustrated in the accompanying figures. However, the style of interactive dialogue between designer and computer is difficult to capture on paper. After selection of a design task from a menu the screen is cleared and display of data follows instantly. For compact presentation in this paper, displays have been presented as a linear dialogue
86
between computer and designer. To provide a clear understanding of results, explanations of available checks and full definition of related parameters may be displayed during design. A list of all design checks currently held by the program may be displayedas shown in Figure 3. Wherever possible, design check assumptions are described under the headings of source, limitations, logic and analyses. A typical display is shown in Figure 4, AVAILABLE CEECI[S 1 COtlPATABI I, ITY Fitting 2 IqTEGR ITY FRAHE HEHBER
,,,~c.
SgSI~CI! LTBX
Cp,xCAX~ c:~eY SHRY SECTION CAXH OIPX c~PY m~RY HNI'X
[4NTY
3 FUIICTPERF 4COST
of
parts
-
flanges
FLGE
SPCS
Hechanism due to hinges Snap sway buckling of PF Lateral buck i in~,, Colabined axial load g ~,lomeut Axial load (failure in X-dir) Axial load (failure in Y-dir) Shear load Combined axial l o a d & momenL Axial load (failure in X-dir) Axial load (failure in Y-dir) Shear load ;~omen t (X-dir) Homen t (Y-d ir )
PFDL
Fouling of specified clear spaces Deflections in portal frame
EST
Estimated cost
Figure 3. Console display of checks available in the program library
computer-aided design
Console d i s p l a y .
* FOR
Explanatory n o t e s .
CHECKS LIST LOGIC RETURN
PRESS l 2 RTN
2 NAHE CHECK FR0+I LIST ** CAXN: Combined a x i a l
- select
CAXH
check
l o a d and moment c a p a c i t y of member - explanation
SOURCE: D r a f t B . S . 5950 e l . 11.7 LIMITS: For I - s ~ c t i o n o n l y Assome= aember bucktea about minor axis LOGIC: For a x i a l load o n l y ( c I . 1 1 . 7 . 1 ) Tension FT < AE*PY Compression FC < AE*PC For SN o n l y on e i t h e r X or ¥ axes 14XABS(~L~)and HEY>ASS(SlY) Semi-coup F / ( AE*PY) ÷ASS(F.~)/,ICX ÷ABS(~PI)/HCY ) 1 . 0 Slender omitted For buckling r e s i s t a n c e (PIAC)IPCX÷MYBIMB ~ 1.0 I f PCY > 0.666*PCK
• • • • •
(F/AG)/pcY÷NYB/NB÷O.5~(F/AG)IPCY~(NCS/HCY)) l.O If
ABS(HY)=O
If
ASS(MY)>0
and
ABS(MX)>0
(PIAG)IPCX+I4XBII4B÷O.5*(PIAG)IPCX*(~XB/14CX) ~ I',0 and ABS(HX)>0
~/SINAX+I4XBI(c*NAY)
/, 1.o
ANALYSIS: A x i a l l o a d s & moments derived f r o ~ a n a l y s i s Of the s t r u c t u r a I s y s t ~ under load, FAILURE OF APPLICATION OF CHECK: "SECTION NOT SUITABLE" *PAUSE IN EXPLANATION OF CHECK
Thus, for symmetrical portal frames, concise input of data may be followed by routines to generate full details of geometry and load. An optional routine is also available to select initial sizes of members based solely on moment carrying capacity. Revision of data with minimal input may be affected in the following categories: member size nodal restraints lateral restraints part geometry (eg haunch description) load on a member
After selection of a particular categor~ t:~e sGrecn is cleared and • ~abular display of related da~a.appears. R~vised'data may then be input. A~er each change within a category the database is reconstimted~ as necessa~,. On~c~mpletion~ of all revisions, prior to any' otl~r opera~ion, the dat~ description is checked for general consistency by the: program and anomalies are pointed out.
- continue s e l e c t i o n o f design o p t i o n s
Figure 4. Console display of logic for a selected check DATA INPUT Data describing the structure and loading details may be input from the keyboard or from a disc file. The designer may review and alter this data at any stage in the design. On input, each main structural member, together with all parts fitted onto it, is described in relation to a previously declared centre-line datum. After selecting a particular category of data to input, the screen is cleared and a compact tabular presentation of data, with headings and prompts, can be created and altered with cursor movement. Data may be input in detail in the following categories: • type of structure, number of datums and restrained nodes • x andy coordinates describing each datum • spaces along datum to be kept clear of attachments • form of restraints to nodes • material design strength, Young's modulus and shear modulus • details of parts and lateral restraints along each datum. Initially the member type (eg universal beam) and size is declared. Then, number and location of lateral restraints as well as parts at each restraint may be declared. A haunch is input as a part, described by type, size, length and depth • details of loads located on members (value, location whether working or factored, dead or live). If the member is declared to be a rafter a concise form of input may be used. On completion of input and prior to any other operation, data describing the structure and loads is checked for validity and consistency. Two options for the routine generation of a structural arrangement have been made available in the prototype program as follows: derivation of geometry and load arrangements for specific types of structure • member size selection based on selected performance criteria.
COMMUNICATION
OF P E R F O R M A N C E
All data available on completion of the design checks may be displayed on the VDU. Various forms of display have been devised to communicate the current state of a design represented by the large amount of data generated by systematic checking. These range from unabridged listings to selections of data devised to assist design decisionmaking, as follows: • • • • •
•
list of checks carried out for the system as a whole and for each datum list of check failures for the system as a whole and for each datum tables for comparison of costs to performance for the structure as a whole and for parts detailed results of computations carried out for design checks analysis results in convenient categories ie for stability, forces at nodes and in members; for deflection, displacements at nodes; for cost, weights of members detailed estimated costs for individual parts and for the complete structure, based on rates held by the computer
Examples of the variety of display produced during typical design work are shown in Figure 5. Tabular displays describing the performance of the structure in comparative terms are instantly available for selection following global checking. The form of display enables results from any type of check to be incorporated in a consistent manner. These displays give access to all parameters and performance Indicators used in checks and are not readily and conveniently created by other types of 'design' program. Displays of check results together with costs are made available, for convenience, in the following categories: • • • •
overall performance compatibility integrity functional performance
•
volume 17 number 2 march 1985
The latter three categories have been identified as a convenient basis for grouping check results for presentation. All checks related to assembly of parts concern com-
87
The g e o m e t r y a n d l o a d a r r a n g e m e n t of a two bay p o r t a l f r a m e has been input u s i n g r o u t i n e data g e n e r a t i o n a n d m e m b e r s h a v e been a d d e d to f o r m a lean-to. 3
6
10
Structure and load arrangement restraints are indicated thus ; a load acts
(lateral Console
at e a c h
display.
* TO
INPUT
RETURN
*
* TO D E R I V E
restraint)
Explanatory
IN D E T A I L USING ROUTINE GENERATION FROM FILE DATA REVISIONS TO T A S K C O N T R O L
& I N P U T L O A D S FOR PORTAL FRAME TRUSS ROUTINE GENERATION MEMBER R E T U R N TO I N P U T
PRESS
1 2 3 4 RTN
LAYOUT
PRESS SIZES
1 2
notes.
- select input of d a t a - see Fig. 3 for t r e e of o p t i o n s
- select routine g e n e r a t i o n of member sizes
3
RTN
*
*PAUSE
SELECTED *PAUSE
CHECKS
CARRIED
OUT
IN T A S K C O N T R O L
* TO O U T P U T
RETURN
,
- routine generation carried out - c h e c k s c a r r i e d out explanatory message
IN T A S K C O N T R O L
CHECKS CARRIED OUT CHECK FAILURES C O S T & P E R F OF P A R T S R E S U L T S OF S E L E C T E D C H E C K S ANALYSES ESTIMATED COSTS TO T A S K C O N T R O L
PRESS
1 2 3 4 5 6 RTN
2
select options for d i s p l a y of r e s u l t s of d e s i g n checks s c r e e n is c l e a r e d p r i o r to s e l e c t e d display select display check failures
CHECK
of
FAILURES c o n c i s e list of check failures
SYSTEM
DATUM
DATUM
1 -
2 -
FAILURE: FAILURE:
BAY BAY
1 2
FAILURE: FAILURE:
MEM MBM
LTBX CAXM
FAILURE: FAILURE:
MEM MEM
LTBX CAXM
full d e t a i l s of c h e c k s m a y be d i s p l a y e d - see Fig. ~(e)
2
3
- console omitted DATUM
7 -
DATUM
8 - i0
*PAUSE
display in f i g u r e
8 FAILURE:
MEM
CAXM
FAILURE: FAILURE:
MEM M~M
LTBX CAXM
IN O U T P U T
Figure 6(a). Sample console display during design of a multi-bay portal frame with lean-to patibility. Those related to the integrity of the structure under load are grouped together. Checks concerning functional performance, such as deflection and fouling of specified cleared spaces are presented together.
88
Performance indicators are used to describe the result of comparisons computed during a design check, overall performance is presented as a list of indicators, one for each most critical check result in each of the three categories
computer-aided design
select options for cost a n d p e r f o r m a n c e of p a r t s
* FOR P E R F O R M A N C E
RETURN
OF P A R T S OVERALL PRESS 1 COMPATABILITY 2 INTEGRITY 3 F U N C T I O N A L PERF 4 SELECTED CHECK RESULTS 5 TO O U T P U T RTN
*
COST
& PERF
FOR
INTEGRITY
OF P A R T S
PART
COST(
)
- critical performance for i n t e g r i t y of p a r t s PERF:STANDARD
SYSTEM FRAME
DATUM
1 -
8698.75 OK 5.90 0.81
SNAP SWAY MECH
1.75 0.62 0.03
LTBX CAXM SHRY
NOT A P P L - critical for each
2 MEMBER
1079.10
- console omitted DATUM
7 -
1079.10 F F 0.02
LTBX CAXM SHRY
1.05 0.47 0.01
LTBX CAXM SHRY
0.79 0.62 0.01
LTBX CAXM SHRY
F:
SNS SNS
SNS:
fails s e c t i o n not suitable
8 - 10 MEMBER
DATUM
499.05
9 - I0 MEMBER
977.93
*PAUSE
IN C O S T & P E R F OF P A R T S
*PAUSE
IN O U T P U T
*PAUSE
IN T A S K
- p r o c e e d to s c r u t i n y of data a n d o p t i o n a l revisions
CONTROL
s e l e c t d i s p l a y of data d e s c r i p t i o n of s t r u c t u r e
2 * TO D I S P L A Y
RETURN
* STATE SIZE KG/M D B WEB T
display in f i g u r e
8 MEMBER
DATUM
indicator check
STRUCTURE & DATUM END R E S T R A I N T & M A T E R I A L DETAILS LOAD DESCRIPTION P R O P E R T I E S OF P A R T S TO T A S K C O N T R O L
DATUM
305.102 25.00 304.80 101.60 5.80 6.80
PRESS
1 2 3 4 5 RTN
1 RO DF AG IX IXN IY
*PAUSE
IN D I S P L A Y
*PAUSE
IN T A S K
7.60 275.80 31.40 4387.00 3962.00 120.00
RX RY ZX ZY D/T
11.82 1.96 287.90 23.60 44.60
SX SY AX AY H J
- select properties of p a r t s - r o u t i n e s e l e c t i o n of member sizes 337.80 37.98 produces a c o m m o n size 2.00 for all 3.50 members 0.03 4.72
CONTROL
1 * TO
INPUT
RETURN
IN D E T A I L USING ROUTINE GENERATION FROM FILE DATA REVISIONS TO T A S K C O N T R O L
PRESS
1 2 3 4 RTN
- select options for r e v i s i o n of data description of s t r u c t u r e
Figure 6(b). Samp~ display during des@nof a mult~bay portal frame with ~an-to adopted. Alternatively, presentation of results for any of the three basic categories described above shows critical indicators from every check carried out in the category.
volume 17 n~Jmber 2 march 1985
Figure 5(b) shows critical performance indicators for all integrity checks carried out for frame and members (eg lateral buckling, combined axial load and moment and
89
* TO
CHANGE
RETURN
FOR
SELECTED
ALTER
MEMBER
LIST
MEMBER SIZE END R E S T R A I N T DATUM DETAILS G E O M E T R Y OF H A U N C H LOADS DISPLAY DATA TO T A S K C O N T R O L
DATUM
REVISED
DATA
SIZE
1 2 3 4 5 6 RTN
REPLACES
THAT
TO C O N T I N U E
DATUM 1 2 3 4
TYPE i0 i0 i0 i0
5
I0
6 7
i0 i0
°
PRESS
EXISTING
PRESS
- select change in m e m b e r s i z e
ESC
SIZE 19 25 25 19 25 25 19
input revised member sizes 19: 4 0 6 " 1 7 8 " 5 4 k g < e s c > on of input
completion
*PAUSE
IN R E V I S I O N
OF
consistency on data
DATA
check
select particular o u t p u t of c h e c k r e s u l t s - see Fig. 3 * FOR
PERFORMANCE
RETURN
COST
& PERF
FOR
OF
PARTS OVERALL PRESS 1 COMPATABILITY 2 INTEGRITY 3 FUNCTIONAL PERF 4 SELECTED CHECK RESULTS 5 TO O U T P U T RTN
INTEGRITY
OF
PART
PARTS
COST(
)
- critical performance for i n t e g r i t y of p a r t s
PERF:STANDARD
SYSTEM FRAME
DATUM
1 -
1564.15 OK 1.48 0.36
SNAP SWAY MECH
0.47 0.47 0.02
LTBX CAXM SHRY
NOT
APPL
2 MEMBER
233.08
console omitted
DATUM
7 -
8 MEMBER
DATUM
233.08 OK 1.22 0.22
LTBX CAXM SHRY
0.47 0.47 0.01
LTBX CAXM SHRY
0.62
LTBX CAXM SHRY
t,~EV
8 - i0 MEMBER
DATUM
49.90
9 - I0 MEMBER
97.79 0.62
0.01 *PAUSE
IN C O S T
& PERF
OF
PARTS
Figure 6(c). Sample display during design of a multi-bay portal frame with lean-to shear for members), Full details of all computations carried out for a given check are shown in alternative displays to those just
90
display in f i g u r e
reselect of data
revision
described. Displays may be used to show performance indicators alongside the identification and Value of parameters used for their derivation as in Figure 5(e).
computer-aided design
* TO
CHANGE
RETURN
MEMBER SIZE END RESTRAINT DATUM DETAILS GEOMETRY OF HAUNCH LOADS DISPLAY DATA 'IX) T A S K C O N T R O L
PRESS
1 2 3 4 5 6 RTN
, -
FOR
SELECTED
ALTER
DATUM
GEOMETRY
OF
DATUM 2 3 5 6
LIST
REVISED
DATA
REPLACES TO
HAUNCH HCH 1 2 1 2
TYPE I0 10 10 10
THAT
CONTINUE
SIZE 25 25 25 25
EXISTING
PRESS L(M) 1.5 1.5 1.5 1.5
ESC D(M) 0.4 0.4 0.4 0.4
*PAUSE
IN R E V I S I O N
OF
select change (addition) of haunches
DATA
-
input
haunches
- < e s c > on c o m p l e t i o n of i n p u t - consistency check on d a t a
DATA DESCRIPTION OF STRUCTURE CHECKS NOT CARRIED OUT *PAUSE
IN T A S K
REVISED
CONTROL - carry
SELECTED *PAUSE * TO
CHECKS
CARRIED
IN T A S K
OUTPUT
RETURN
out
checks
OUT
CONTROL
CHECKS CARRIED OUT CHECK FAILURES COST & PERF OF PARTS RESULTS OF SELECTED CHECKS ANALYSES ESTIMATED COSTS TO TASK CONTROL
PRESS
1 2 3 4 5 6 RTN
2
select check results - see Fig. 3 s c r e e n is c l e a r e d p r i o r to s e l e c t e d display
list check failures CHECK
FAILURES
SYSTEM
DATUM
4 -
5
DATUM
7 -
8
*PAUSE * TO
FAILURE: FAILURE:
BAY BAY
1 2
FAILURE:
MEM
CAXM
FAILURE:
MEM
CAXM
- having improved design detailed r e s u l t s of c h e c k s are selected
IN O U T P U T
OUTPUT
SELECTED
RETURN
LIST OF TO O U T P U T
CHECK RESULTS PARAMETERS CHECKS CARRIED
PRESS
1 2 3 RTN
OUT
- select detailed r e s u l t s of c h e c k s
,
* SELECT
1:FRAMES 3:MEMBERS
2:FRAME-BAY 4:MEMBER-PORTION 6:PARAMETERS
5:MEMBER-SECTION RTN:RETURN
1 **
FACTORS
& PARAMETERS
COMPATABILITY
OF
FOR
ALL
BAYS
OF
- s e l e c t d e t a i l s of c h e c k s on f r a m e s showing failures
FRAME
PARTS DATUM DATUM DATUM DATUM DATUM DATUM DATUM DATUM DATUM
1 2 3 4 5 6 7 8 9
2 3 5 5 6 8 8 - 10 - 10
OK OK OK OK OK OK OK OK OK
Figure 6(d). Sample display during design of a multi-bay portal frame with lean-to They may be selected by frame, bay, members, portion of member or cross section. Comments indicate when a
volume 17 number 2 march 1985
relevant check is, in fact, inapplicable. After a command requesting display, and before presentation of fresh design
91
INTEGRITY SNAP-SWAY
CHECKS
BAY
FOR
BAY
FAILS
FUNCTIONAL
** F A C T O R S
:
45.5
/ 30.5
: (SPAN/RD)/FY
1.49
:
45.5
/ 30.5
: (SPAN/RD)/FY
FAILS
PERFORMANCE
T O P OF S T A N C H I O N : N O D E
PERF
: DEFL(M)
/ PERM DEFL(M)
2 5 8
0.22 0.01 0.23
: -0.006 : 0.000 : 0.006
/ / /
MIDSPAN:NODE
PERF
: DEFL(M)
/ PERM DEFL(M)
3 6
0.89 0.86
: :
/ /
ROOF
*SELECT
1.49 2
SWAY
IN C H E C K
*SELECT
FRAME
i SWAY
*PAUSE
PORTAL
v a l u e s of indicator and parameters
0.020 0.020
2:FRAME-BAY 4:MEMBER-PORTION 5:MEMBER-SECTION 6:PARAMETERS RTN:RETURN
NUMBER
& PARAMETERS
COMPATABILITY
-
RESULTS
I:FRAMES 3:MEMBERS
MEMBER
-0.018 -0.017
0.027 0.027 0.027
- select further detailed results
4 FOR M~4BER
4 -
5
OF P A R T S DATUM
4 -
5
OK
INTEGRITY
-
MEMBER PO
*LTBX
OK
* CAXM
FALLS
full d e t a i l s of all i n d i c a t o r s and parameters
1 : MOMENTS
PO
REVERSE
OVER
PORTION
i RPM
0.88 0.55 0.23
: : :
176.6 / 200.0 : L A M D A X / S R 0.001*AY*(LAMDAX-LAMDXO) 54.6 / 240.0 : P C X / P Y
0.36 0.ii 0.82 1.22 0.01
: : : : :
0.01
•
X: 1003.? Y: 175.6 72.7 / 200.0 : LAMDAY/SR 0.001*AY*(LAMDAY-LAMDYO) 196.4 / 240.0 : PCY/PY O.OO7*(LAMDL-LAMDE) 0.5 / 240.9 : M Y / M C Y
MEMBER * SHRY *PAUSE
IN C H E C K
*PAUSE
IN O U T P U T
OK -0.1 /
631.9
: QY/PQ
RESULTS
6 ESTIMATE
COSTS
FOR S T R U C T U R E
- list of e s t i m a t e d costs
PART DATUM
i -
2
DATUM
2 -
3
MEMBER
384.15
MEMBER HAUNCH
179.30 64.84 - console omitted
DATUM
8 -
i0
DATUM
9 -
i0
TOTAL
MEMBER
49.90
MEMBER
977.93
ESTIMATE =
*PAUSE
IN O U T P U T
*PAUSE
IN T A S K
display in f i g u r e
2273.71
CONTROL
- design
continues
Figure 6(e). Sample display during design of a multi-bay portal frame with lean-to 92
computer-aided design
information, the screen is cleared and the cursor is moved to the top left hand corner. Redundant information is rapidly replaced by that currently selected. At the end of each operation the program pauses awaiting immediate selection of a further design option. Relevant options following a particular display of results are presented in a manner that emphasises the designer's control of the computer. Revision of the structural arrangement is eased by convenient selective perusal of the wide range of design check information available.
CONCLUSIONS Consideration of the design process suggests that an effective aid to design decision-making must provide for scrutiny of relevant performance indicators related to design checks. Also, information describing the detailed basis of design checks should be readily available to the designer, preferably as part of the software. A computer design aid has been described which provides assistance in the selection and assessmentof structural arrangements for steel frameworks. A particular technique has been devised to integrate the tasks of handling design selection and assessmentinto one computerized aid. This technique enables virtually any design check, including cost, to be incorporated in a consistent manner. The effectiveness of the computer aid stems from the facilities provided both to alter and scrutinize a database describing structural layout, loading and performance, together with the ability to select and organize a large number of relevant design checks. To this end, a convenient basis for selective review of design options and information has been devised. A modular program structure permits ready incorporation of additional design checks for a variety of structural elements. Also the checks may be devised to suit individual preferences of the designer. Virtually all limit states can be checked systematically using a computing aid of the type described. Information to determine applicable checks need not be generated manually by the designer. Selecting checks for a structure is replaced by specifying the type of structure to be designed. Reduction in the amount of data to be communicated leads to considerable saving in design time and effort. Arrangements of design data not readily generated by other types of program may be displayed in rapid succession to assist decision making, following the single global check on performance. In particular, performance indicators, together with costs, may be compared for all design checks carried out. For a given design, display of selected check
volume 17 number 2 march 1985
results is virtually instantaneous. Computational delay occurs only during routine generation of initial designs from concise input data or during the brief phase in which all checks are systematically carried out for the defined design. The program offers a viable and much more powerful alternative to packages based essentially on manual design methods. For effective use, each designer would require constant and convenient accessto such a facility. The improved potential of small computers should allow this requirement to be met in the near future.
ACKNOWLEDGEMENTS Work related to this paper was carried out in the course of a SERC Total Technology scheme of study at the Department of Civil Engineering, University of Leeds. Views on current and future needs relating to CAD in structural steelwork were gratefully received from member firms and technical staff of the British Constructional Steelwor'k Association.
REFERENCES 1 Beeby, A W'Reinforced concrete design calculations using small computers - DECIDE' 5truct. Eng. Vol 56A No 10 (October 1978) pp 287-289 2 Yeadon, R E 'The interactive design of portal framed buildings' Struct. Eng. Vol 57A No 9 (September 1979) pp 288-292 3 Laxon, W R, Malby, K H, Mounfford, D H and Shuttleworth, B T 'Automatic design of structural steelwork' Comput.-Aided Des. Vol 12 No 1 (January 1980) pp 35-42 4 Morris, L J and Randell, A L Plastic Design Constrado (1975)
5 Croft, D D 'The GLADYS computer system for the design of reinforced concrete elements' 5truct. Eng. Vol 56A No 10 (October 1978) pp 282-286 6 Moore, M G and Brotton, D M 'Interactive design and detailing of structural steelwork connections using a computer' 5truct. Eng. Vol 52 No 4 (April 1974) pp 133-142 7 British Standards Institution Draft standard specification for the structural use o f steelwork in buildings BSI London (1977) also Section 12 and associated appendices BSI London (1979)
93
Microcomputer programs available to assist the design of specific classes of building structure are generally based on the manual design process. That is, critical design factors are considered in a sequence known from experience to be expeditious for designing the type of structure in question. Design calculations are handled in separate modules which reflect traditional code of practice design of elements. Hand calculation methods are mechanized and the user is simply required to supply data at predetermined points in a conventional design sequence. It is argued 1 that this method simplifies both program operation and checking of resuIts. Computer-aided design of steelwork structures is usually based on this approach Programs for the design of portal frames 2'3 commonly use a design procedure4 proposed for manual design. To improve a design, some programs allow certain data to be modified and rerun. Such design changes must draw inspiration from the limited information displayed during program runs. Thus in Yeadon 2, a design program module determines a collapse mechanism for the frame and carries out an initial selection of members, essentially following the procedure described by Morris and Randell 4 . Using other modules, the designer may opt to check rafter, haunch and stanchion stability and thus determine the position of necessary lateral restraints. Further self-contained programs may be used to check deflection and design elements such as purlins and rails. In Laxon et al 3 design selection is carried out to preset Structural Design Information Software, Leeds, U K
*Department of Civil Engineering,University of Leeds,Leeds,UK
volume 17 number :2 march 1985
criteria, without interaction. Design feedback is restricted to lists of quantities and costs, with optional listing of formal design calculations as design proceeds. In an approach, based primarily on preconceived solutions, the relationship of designer to computer is supplementary. A style of interaction limited essentially to response to prompts for information has been evolved. A program developed according to this approach for the design of structural elements s characterizes control of the computer by the use of the command GO and the role of the user by the command HELP. When the computer halts at some stage of a predetermined design process it waits for a command to proceed and offers prompts to help the user. This simple style of interaction is widely used in computeraided structural design. As a basis for interactive design, the above method of operation has shortcomings. Clearly, the designer should be in control of design strategy and the style of data presentation and commands should reinforce this. The form of presentation, based on routine output of information for each element as calculations proceed, is incompatible with this need as it makes spontaneous scrutiny of information at any of the design stages impossible. Results of protracted and repetitive calculations cannot be compared easily on scrolled screen display or paper listings. Limited ability to interact and access the current state of variables and the imposition of specific forms of design solution inhibit innovative design. Ideally, the computer should present information in a form most suited to assist design decision-making without undue delay from data processing activity. To enable changes in design strategy to be made, screen displays should allow design options to be readily identified. This requires procedures for handling and presenting design data which are different from those suited to achievement of preconceived designs or production of formal design documents. To this end, graphical computer display alongside textual presentation of values of certain design variables has been used by Moore and Brotton 6. Using informative interaction, their program simplifies the design of skewed steel beam-to-column connections, particularly in ensuring geometric compatibility of parts. It is clear that computerized design tasks should not dictate design strategy. There are few logical paths in conceptual design and it is important that the designer be allowed to explore novel arrangements. To this end, routine derivation of data must be combined with a facility to collate useful and perhaps unique sets of data for scrutiny. Programs based essentially on manual design procedures cannot be readily adapted to present the extensive design
0010-4485/85/0:20083-I I $03.00 © 1985 Butterworth & Co (Publishers) Ltd
83
information that would aid innovative design. This paper describes a method of computer assistance that extends the scope of information available for scrutiny during design. A program has been developed to ascertain the extent of interaction delays, ease of operation and influence on the design process. The prototype program addresses itself to steel framework design, though the principles adopted may be applied to structures incorporating other materials. It was conceived and written in anticipation of the powerful, low-cost microcomputers now available. The program aims to provide a total review of the performance of a selected structural arrangement, with convenient interactive facilities for carrying out a wide variety of design tasks. To do this, design checks are handled in a manner that is qualitatively different from manual design methods. Techniques adopted for the generation and presentation of information are based on a preliminary classification of data handled during design checking, as outlined below.
Outline configuration
STANDARD Specification scope Definition of part
Definition of parameters
Definition of mes~Jre of beheviour
Definition of performance
CHARACTERISTICS OF THE DESIGN PROCESS Two key activities in design are selecting material layout and checking that all relevant standards (including those concerning function and cost) are satisfied. Occasionally the two activities may be combined using routine procedures based on experience of handling critical design factors. Thus, steel section sizes may be selected considering a minimum collapse load factor only. However, further modifications are usually necessary when designing portions of the structure excluded from the routine procedure. For example, additional forces may arise from incidental bracing. Final review of the complete design is invariably necessary because routine procedures consider only a selection of relevant performance critiera. The assessment of the performance of a structural arrangement comprises two basic steps: •
identification of a basically similar arrangement which has been dealt with before • assessmentof aspects of its behaviour using convenient formulae to interpolate between available test data Overall, this can be called a design check. Access to information and design procedures from tests or previous applications is basic to this process. The scope of such information inevitably extends beyond that available in standard specifications and codes of practice. A designer will be aware of the following inherent limitations of design checks: • a standard check is applicable only to a limited range of configurations and material types • the required degree of precision necessary for parameters used in checks is not always readily understood • analysis routines invariably involve simplifications • alternative checks are often available for assessing performance and may yield different results To assist design decision-making, key features of a check should ideally be available for scrutiny along with results to enable the full implications to be appreciated. Figure 1 shows the activities and data flows involved in a structural design check. In practice, when performance is satisfactory, differences between the model contained in the standard and the proposed design configuration are often disregarded. The overriding objective in carrying out a check is to make easy further decision and action. Only a limited
84
Obtain relevant standard Propo~d confi~ration
Model configuration to standard
Modelled configuration Definition of material type, size and service conditions
Calculate data required for check
Calculated data required for check
Analyse model for behaviour in service
Performance indicators
Compute performance indicators
Judge performance and validity of model"
+ -- n~.. m C~ iLv )
informs activity store data source of data sequence of activities
Figure 1. Activities and information involved in a design check proportion of the total range of structural design checks is applicable to a given design. Within this limited proportion, only a small number of checks are likely to be critical. The effectiveness of a design check depends on its convenience with regard to data handling and also on a clear definition of the model incorporated and its reliability when correctly applied. Accuracy of results is not necessarily crucial.
Selecting a structural arrangement Design procedures evolve through accumulated experience of application. Short cuts are frequently used in the manual design process when checks known to be noncritical for the structure may be omitted. For example, certain design criteria are formulated in Morris and Randell4 for typical steel portal frame structures under load. Codes of practice and design guides permit routine selection of certain performance and manufacturing standards once element detail has been decided. At any point in design, choice of action is restricted to a small proportion of all the design tasks which must be undertaken in the course of the design. To determine possible courses of action requires access to and a review of relevant tasks and design information created so far in the design. Design can start with any selected configuration and does not follow a predetermined path. Initially, in the selection process, a comparison is made between present and previous design configurations, using performance data from design checks. The degree of comparison depends on the complexity of the design checks. Substitution of one part or more is then made and a new comparison carried out. Indicators of structural performance, together with cost, are used as the basisfor assessingthe merits of an innovation
computer-aided design
in design. An indicator might be scalar (for example, the proportion of working to permitted deflection at a point in a structure) or might simply show success or failure (the outcome of a design check). Judgement on whether standards are met requires consideration of all relevant indicators. To improve the performance of a scheme, a designer modifies the structure, selecting from the range of material available. The overall effect of alterations on the performance of the structure may not be apparent without considering all available data in combination. In practice the extent of this picture depends on the checks actually selected by the designer. It is clearly advantageous to have a total picture of the current scheme to assist further selection of material.
FUNDAMENTAL FEATURES OF A COMPUTER DESIGN AID Ideally, decision-making in design requires ready access to results of design checks carried out for a previous trial. However, results generated from a large number of design checks cannot be displayed simultaneously on a visual display screen. In practice, appropriate combinations of information need to be readily available for perusal. But, simply displaying results as calculations proceed severely limits useful juxtapositioning of data, unless calculations are repeated. In fact, display of results as calculations proceed is not necessary provided that all checks can be carried out rapidly and key results stored for attention later. To handle and present results of design checks in this way requires both an efficient data storage/retrieval system and new arrangements for communication of design information. A prototype computer program has been developed to assessthe handling of design checks by such means. The objective of the program was to assist the selection of member and haunch elements of a portal frame. Appropriate design checks from various sources, including the Draft BS 59507 (the scheduled replacement to BS 449) have been incorporated. Data used for checks is stored and retrieved by the computer in the categories summarized in Figure 1. Design checks are handled by the computer in a manner that provides a total review of performance. Selection and assessment of design checks are integrated in one computer aid through the adoption of the following technique for handling design information. After the data description of a structure has been input, design checks held in the program library can be selected and carried out automatically without display of results. The type of structure defined in the input specification determines which checks are required. To determine particular application of checks relating to the whole or part of the structure appropriate analyses are carried out and systematically inspected. All members and parts are checked sequentially and resulting design parameter values retained for optional viewing later. In addition, checks on behaviour of the structure as a whole are carried out. Rules of thumb or 'design insight' for identifying checks applicable to a particular type of structure are not used. For example, maximum shear in a simply supported beam is found through a search of analysis results, not by using a knowledge of its likely location. To incorporate the latter in a program would require either a previous declaration of element type or an automatic analysis to determine that it was a simply supported beam. The program may be regarded as a convenient operating
volume 1 ? number 2 march 1985
system for computerized design tasks. Its modular basis facilitates extension to cover many checks, including cost, for a variety of types of part. Control of subroutines .for parameter evaluation, design checks, display of results and filing of data is structured to allow easy insertion of further design features. Interactive commands for the scrutiny of design options and data are handled by a separate set of routines. A database representing full details of the design, both in terms of structural arrangement and performance, has been devised to exploit the method adopted for handling design checks. After constructing the database to accommodate detailed methods of data input and scrutiny of results for design decision-making, concise methods of handling data were added. Further methods and refinements can be developed using the adopted database. The program is fully operational, with error trapping and recovery procedures. It requires an interactive facility providing fast computing response and rapid access to stored data and was developed using a VAX 11/780 computer. However, the modular structure adopted was conceived to suit microcomputer operating systems.
DESIGN FACILITIES PROVIDED BY THE PROGRAM For convenient accessto a range of facilities that handle design checks for a complete structure, an executive system of program control is used. Control is passed back and forth along a tree of linked options, allowing design to proceed quickly by repeated modification and appraisal. Standard design tasks may be carried out in particular design situations at the will of the designer. This includes such tasks as changing the configuration of parts in a structure and display of full cost estimates. On command, all relevant checks held in the library of routines are carried out for the complete structure. Although this is the longest operation undertaken by the program, the delay is well within acceptable limits for interactive operation. For example, all checks for a threebay portal frame with haunches are carried out in about ten seconds. After this global operation, the designer may select displays of design information. Access to the results of checks is virtually instantaneous. To ease selection for the designer, a set of basic options for carrying out checks, displaying results, filing etc is provided as follows: • display structure and loading details • select and carry out relevant checks from the program library • display results oi~design checks • input or revise the description of the structure and loading details • display schedule and cost of available material • display concise definition of a nominated check or procedure • select and display definition of a specific parameter used in a check • file results of design checks for listing later or for the record After selection of a particular main option a set of secondary options may be displayed for the convenience of the designer. The tree of available options i~, shown in Figure 2. Access to some main options is provided at several points in the tree where appropriate.
85
tructural type atum details lear spaces nd restraints ~r-~ Material /~ [Details / I Load description / tDisplay data Start here Task control:
/
/
/
/
FEnter in detail ~ ..~ Derive using routine g e n e r a t i o n ~ L a y o u t and loads for portal frame truss I Obtain from f i l e ~ L.Member sizes I Revise data
Input data ---/ Display data ~ Carry out checks ~ Display check results----~ File output for printing \ File data,for p r i n t i n g \ Display information 7 \ Stop / \
/ / / / /
r-Mem r
-
~-
~
'FStructure and datum ] End restraint and material Details ~ L o I Load description [_Properties of parts
]End restraint "",----I Datum I Geometry a d s description l_Display data
FCheckscarried out [Check failures ~ Cost and ;p~rf~rmance of parts [Selected check results \ I Analyses \\ [_Estimated costs \ \ \ \ \ \ \ \ [List of available checks \ \
o''o
Z--- I Parameters---..___~List of definitions L_Material~ L_Derivation
"~-...__[-Types and forms I_Sizes available
[Overall I Compafibifi~y l Integrity [Functional performance l_Selected check results F 1 : Frames 2: Frame-bay /-1 3: Members 4: Member-portion / L_5:Member'section
\ Vc:::m : vau0, \
LCheckscarried out
~ ]-'Stability ~ _ ~ ~Defiection L_Costs
forces at nodes forces in members displacement of modes Weights of members
Figure 2. The tree o f design options contained in the program. Control may be passed back and forth between lists as indicated
To achieve rapid selection of an option, selection is made using a single digit code, as shown in the examples of screen output. The lists of options and codes may be suppressed if desired. On completion of a particular option, control is usually returned to the current list in use and the program pauses. Another option may then be chosen or the series redisplayed. A single keystroke returns control to the previous series. In practice, digital commands are assimilated quickly with experience and the program may be used without displaying options. As already mentioned, it is not possible to present all the design information from the global checking operation in one static display. Therefore the description of the structure and loading details, together with results of checks carried out have been broken down into convenient displays which the designer may peruse at will. The form and content of display strictly relate to the needs of structural design and are not merely a dump of data from memory, Data input and communication of results are described below and illustrated in the accompanying figures. However, the style of interactive dialogue between designer and computer is difficult to capture on paper. After selection of a design task from a menu the screen is cleared and display of data follows instantly. For compact presentation in this paper, displays have been presented as a linear dialogue
86
between computer and designer. To provide a clear understanding of results, explanations of available checks and full definition of related parameters may be displayed during design. A list of all design checks currently held by the program may be displayedas shown in Figure 3. Wherever possible, design check assumptions are described under the headings of source, limitations, logic and analyses. A typical display is shown in Figure 4, AVAILABLE CEECI[S 1 COtlPATABI I, ITY Fitting 2 IqTEGR ITY FRAHE HEHBER
,,,~c.
SgSI~CI! LTBX
Cp,xCAX~ c:~eY SHRY SECTION CAXH OIPX c~PY m~RY HNI'X
[4NTY
3 FUIICTPERF 4COST
of
parts
-
flanges
FLGE
SPCS
Hechanism due to hinges Snap sway buckling of PF Lateral buck i in~,, Colabined axial load g ~,lomeut Axial load (failure in X-dir) Axial load (failure in Y-dir) Shear load Combined axial l o a d & momenL Axial load (failure in X-dir) Axial load (failure in Y-dir) Shear load ;~omen t (X-dir) Homen t (Y-d ir )
PFDL
Fouling of specified clear spaces Deflections in portal frame
EST
Estimated cost
Figure 3. Console display of checks available in the program library
computer-aided design
Console d i s p l a y .
* FOR
Explanatory n o t e s .
CHECKS LIST LOGIC RETURN
PRESS l 2 RTN
2 NAHE CHECK FR0+I LIST ** CAXN: Combined a x i a l
- select
CAXH
check
l o a d and moment c a p a c i t y of member - explanation
SOURCE: D r a f t B . S . 5950 e l . 11.7 LIMITS: For I - s ~ c t i o n o n l y Assome= aember bucktea about minor axis LOGIC: For a x i a l load o n l y ( c I . 1 1 . 7 . 1 ) Tension FT < AE*PY Compression FC < AE*PC For SN o n l y on e i t h e r X or ¥ axes 14X
• • • • •
(F/AG)/pcY÷NYB/NB÷O.5~(F/AG)IPCY~(NCS/HCY)) l.O If
ABS(HY)=O
If
ASS(MY)>0
and
ABS(MX)>0
(PIAG)IPCX+I4XBII4B÷O.5*(PIAG)IPCX*(~XB/14CX) ~ I',0 and ABS(HX)>0
~/SINAX+I4XBI(c*NAY)
/, 1.o
ANALYSIS: A x i a l l o a d s & moments derived f r o ~ a n a l y s i s Of the s t r u c t u r a I s y s t ~ under load, FAILURE OF APPLICATION OF CHECK: "SECTION NOT SUITABLE" *PAUSE IN EXPLANATION OF CHECK
Thus, for symmetrical portal frames, concise input of data may be followed by routines to generate full details of geometry and load. An optional routine is also available to select initial sizes of members based solely on moment carrying capacity. Revision of data with minimal input may be affected in the following categories: member size nodal restraints lateral restraints part geometry (eg haunch description) load on a member
After selection of a particular categor~ t:~e sGrecn is cleared and • ~abular display of related da~a.appears. R~vised'data may then be input. A~er each change within a category the database is reconstimted~ as necessa~,. On~c~mpletion~ of all revisions, prior to any' otl~r opera~ion, the dat~ description is checked for general consistency by the: program and anomalies are pointed out.
- continue s e l e c t i o n o f design o p t i o n s
Figure 4. Console display of logic for a selected check DATA INPUT Data describing the structure and loading details may be input from the keyboard or from a disc file. The designer may review and alter this data at any stage in the design. On input, each main structural member, together with all parts fitted onto it, is described in relation to a previously declared centre-line datum. After selecting a particular category of data to input, the screen is cleared and a compact tabular presentation of data, with headings and prompts, can be created and altered with cursor movement. Data may be input in detail in the following categories: • type of structure, number of datums and restrained nodes • x andy coordinates describing each datum • spaces along datum to be kept clear of attachments • form of restraints to nodes • material design strength, Young's modulus and shear modulus • details of parts and lateral restraints along each datum. Initially the member type (eg universal beam) and size is declared. Then, number and location of lateral restraints as well as parts at each restraint may be declared. A haunch is input as a part, described by type, size, length and depth • details of loads located on members (value, location whether working or factored, dead or live). If the member is declared to be a rafter a concise form of input may be used. On completion of input and prior to any other operation, data describing the structure and loads is checked for validity and consistency. Two options for the routine generation of a structural arrangement have been made available in the prototype program as follows: derivation of geometry and load arrangements for specific types of structure • member size selection based on selected performance criteria.
COMMUNICATION
OF P E R F O R M A N C E
All data available on completion of the design checks may be displayed on the VDU. Various forms of display have been devised to communicate the current state of a design represented by the large amount of data generated by systematic checking. These range from unabridged listings to selections of data devised to assist design decisionmaking, as follows: • • • • •
•
list of checks carried out for the system as a whole and for each datum list of check failures for the system as a whole and for each datum tables for comparison of costs to performance for the structure as a whole and for parts detailed results of computations carried out for design checks analysis results in convenient categories ie for stability, forces at nodes and in members; for deflection, displacements at nodes; for cost, weights of members detailed estimated costs for individual parts and for the complete structure, based on rates held by the computer
Examples of the variety of display produced during typical design work are shown in Figure 5. Tabular displays describing the performance of the structure in comparative terms are instantly available for selection following global checking. The form of display enables results from any type of check to be incorporated in a consistent manner. These displays give access to all parameters and performance Indicators used in checks and are not readily and conveniently created by other types of 'design' program. Displays of check results together with costs are made available, for convenience, in the following categories: • • • •
overall performance compatibility integrity functional performance
•
volume 17 number 2 march 1985
The latter three categories have been identified as a convenient basis for grouping check results for presentation. All checks related to assembly of parts concern com-
87
The g e o m e t r y a n d l o a d a r r a n g e m e n t of a two bay p o r t a l f r a m e has been input u s i n g r o u t i n e data g e n e r a t i o n a n d m e m b e r s h a v e been a d d e d to f o r m a lean-to. 3
6
10
Structure and load arrangement restraints are indicated thus ; a load acts
(lateral Console
at e a c h
display.
* TO
INPUT
RETURN
*
* TO D E R I V E
restraint)
Explanatory
IN D E T A I L USING ROUTINE GENERATION FROM FILE DATA REVISIONS TO T A S K C O N T R O L
& I N P U T L O A D S FOR PORTAL FRAME TRUSS ROUTINE GENERATION MEMBER R E T U R N TO I N P U T
PRESS
1 2 3 4 RTN
LAYOUT
PRESS SIZES
1 2
notes.
- select input of d a t a - see Fig. 3 for t r e e of o p t i o n s
- select routine g e n e r a t i o n of member sizes
3
RTN
*
*PAUSE
SELECTED *PAUSE
CHECKS
CARRIED
OUT
IN T A S K C O N T R O L
* TO O U T P U T
RETURN
,
- routine generation carried out - c h e c k s c a r r i e d out explanatory message
IN T A S K C O N T R O L
CHECKS CARRIED OUT CHECK FAILURES C O S T & P E R F OF P A R T S R E S U L T S OF S E L E C T E D C H E C K S ANALYSES ESTIMATED COSTS TO T A S K C O N T R O L
PRESS
1 2 3 4 5 6 RTN
2
select options for d i s p l a y of r e s u l t s of d e s i g n checks s c r e e n is c l e a r e d p r i o r to s e l e c t e d display select display check failures
CHECK
of
FAILURES c o n c i s e list of check failures
SYSTEM
DATUM
DATUM
1 -
2 -
FAILURE: FAILURE:
BAY BAY
1 2
FAILURE: FAILURE:
MEM MBM
LTBX CAXM
FAILURE: FAILURE:
MEM MEM
LTBX CAXM
full d e t a i l s of c h e c k s m a y be d i s p l a y e d - see Fig. ~(e)
2
3
- console omitted DATUM
7 -
DATUM
8 - i0
*PAUSE
display in f i g u r e
8 FAILURE:
MEM
CAXM
FAILURE: FAILURE:
MEM M~M
LTBX CAXM
IN O U T P U T
Figure 6(a). Sample console display during design of a multi-bay portal frame with lean-to patibility. Those related to the integrity of the structure under load are grouped together. Checks concerning functional performance, such as deflection and fouling of specified cleared spaces are presented together.
88
Performance indicators are used to describe the result of comparisons computed during a design check, overall performance is presented as a list of indicators, one for each most critical check result in each of the three categories
computer-aided design
select options for cost a n d p e r f o r m a n c e of p a r t s
* FOR P E R F O R M A N C E
RETURN
OF P A R T S OVERALL PRESS 1 COMPATABILITY 2 INTEGRITY 3 F U N C T I O N A L PERF 4 SELECTED CHECK RESULTS 5 TO O U T P U T RTN
*
COST
& PERF
FOR
INTEGRITY
OF P A R T S
PART
COST(
)
- critical performance for i n t e g r i t y of p a r t s PERF:STANDARD
SYSTEM FRAME
DATUM
1 -
8698.75 OK 5.90 0.81
SNAP SWAY MECH
1.75 0.62 0.03
LTBX CAXM SHRY
NOT A P P L - critical for each
2 MEMBER
1079.10
- console omitted DATUM
7 -
1079.10 F F 0.02
LTBX CAXM SHRY
1.05 0.47 0.01
LTBX CAXM SHRY
0.79 0.62 0.01
LTBX CAXM SHRY
F:
SNS SNS
SNS:
fails s e c t i o n not suitable
8 - 10 MEMBER
DATUM
499.05
9 - I0 MEMBER
977.93
*PAUSE
IN C O S T & P E R F OF P A R T S
*PAUSE
IN O U T P U T
*PAUSE
IN T A S K
- p r o c e e d to s c r u t i n y of data a n d o p t i o n a l revisions
s e l e c t d i s p l a y of data d e s c r i p t i o n of s t r u c t u r e
2 * TO D I S P L A Y
RETURN
* STATE SIZE KG/M D B WEB T
display in f i g u r e
8 MEMBER
DATUM
indicator check
STRUCTURE & DATUM END R E S T R A I N T & M A T E R I A L DETAILS LOAD DESCRIPTION P R O P E R T I E S OF P A R T S TO T A S K C O N T R O L
DATUM
305.102 25.00 304.80 101.60 5.80 6.80
PRESS
1 2 3 4 5 RTN
1 RO DF AG IX IXN IY
*PAUSE
IN D I S P L A Y
*PAUSE
IN T A S K
7.60 275.80 31.40 4387.00 3962.00 120.00
RX RY ZX ZY D/T
11.82 1.96 287.90 23.60 44.60
SX SY AX AY H J
- select properties of p a r t s - r o u t i n e s e l e c t i o n of member sizes 337.80 37.98 produces a c o m m o n size 2.00 for all 3.50 members 0.03 4.72
1 * TO
INPUT
RETURN
IN D E T A I L USING ROUTINE GENERATION FROM FILE DATA REVISIONS TO T A S K C O N T R O L
PRESS
1 2 3 4 RTN
- select options for r e v i s i o n of data description of s t r u c t u r e
Figure 6(b). Samp~ display during des@nof a mult~bay portal frame with ~an-to adopted. Alternatively, presentation of results for any of the three basic categories described above shows critical indicators from every check carried out in the category.
volume 17 n~Jmber 2 march 1985
Figure 5(b) shows critical performance indicators for all integrity checks carried out for frame and members (eg lateral buckling, combined axial load and moment and
89
* TO
CHANGE
RETURN
FOR
SELECTED
ALTER
MEMBER
LIST
MEMBER SIZE END R E S T R A I N T DATUM DETAILS G E O M E T R Y OF H A U N C H LOADS DISPLAY DATA TO T A S K C O N T R O L
DATUM
REVISED
DATA
SIZE
1 2 3 4 5 6 RTN
REPLACES
THAT
TO C O N T I N U E
DATUM 1 2 3 4
TYPE i0 i0 i0 i0
5
I0
6 7
i0 i0
°
PRESS
EXISTING
PRESS
- select change in m e m b e r s i z e
ESC
SIZE 19 25 25 19 25 25 19
input revised member sizes 19: 4 0 6 " 1 7 8 " 5 4 k g < e s c > on of input
completion
IN R E V I S I O N
OF
consistency on data
DATA
check
PERFORMANCE
RETURN
COST
& PERF
FOR
OF
PARTS OVERALL PRESS 1 COMPATABILITY 2 INTEGRITY 3 FUNCTIONAL PERF 4 SELECTED CHECK RESULTS 5 TO O U T P U T RTN
INTEGRITY
OF
PART
PARTS
COST(
)
- critical performance for i n t e g r i t y of p a r t s
PERF:STANDARD
SYSTEM FRAME
DATUM
1 -
1564.15 OK 1.48 0.36
SNAP SWAY MECH
0.47 0.47 0.02
LTBX CAXM SHRY
NOT
APPL
2 MEMBER
233.08
console omitted
DATUM
7 -
8 MEMBER
DATUM
233.08 OK 1.22 0.22
LTBX CAXM SHRY
0.47 0.47 0.01
LTBX CAXM SHRY
0.62
LTBX CAXM SHRY
t,~EV
8 - i0 MEMBER
DATUM
49.90
9 - I0 MEMBER
97.79 0.62
0.01 *PAUSE
IN C O S T
& PERF
OF
PARTS
Figure 6(c). Sample display during design of a multi-bay portal frame with lean-to shear for members), Full details of all computations carried out for a given check are shown in alternative displays to those just
90
display in f i g u r e
reselect of data
revision
described. Displays may be used to show performance indicators alongside the identification and Value of parameters used for their derivation as in Figure 5(e).
computer-aided design
* TO
CHANGE
RETURN
MEMBER SIZE END RESTRAINT DATUM DETAILS GEOMETRY OF HAUNCH LOADS DISPLAY DATA 'IX) T A S K C O N T R O L
PRESS
1 2 3 4 5 6 RTN
, -
FOR
SELECTED
ALTER
DATUM
GEOMETRY
OF
DATUM 2 3 5 6
LIST
REVISED
DATA
REPLACES TO
HAUNCH HCH 1 2 1 2
TYPE I0 10 10 10
THAT
CONTINUE
SIZE 25 25 25 25
EXISTING
PRESS L(M) 1.5 1.5 1.5 1.5
ESC D(M) 0.4 0.4 0.4 0.4
IN R E V I S I O N
OF
select change (addition) of haunches
DATA
-
input
haunches
- < e s c > on c o m p l e t i o n of i n p u t - consistency check on d a t a
IN T A S K
REVISED
CONTROL - carry
SELECTED *PAUSE * TO
CHECKS
CARRIED
IN T A S K
OUTPUT
RETURN
out
checks
OUT
CONTROL
CHECKS CARRIED OUT CHECK FAILURES COST & PERF OF PARTS RESULTS OF SELECTED CHECKS ANALYSES ESTIMATED COSTS TO TASK CONTROL
PRESS
1 2 3 4 5 6 RTN
2
select check results - see Fig. 3 s c r e e n is c l e a r e d p r i o r to s e l e c t e d display
list check failures CHECK
FAILURES
SYSTEM
DATUM
4 -
5
DATUM
7 -
8
*PAUSE * TO
FAILURE: FAILURE:
BAY BAY
1 2
FAILURE:
MEM
CAXM
FAILURE:
MEM
CAXM
- having improved design detailed r e s u l t s of c h e c k s are selected
IN O U T P U T
OUTPUT
SELECTED
RETURN
LIST OF TO O U T P U T
CHECK RESULTS PARAMETERS CHECKS CARRIED
PRESS
1 2 3 RTN
OUT
- select detailed r e s u l t s of c h e c k s
,
* SELECT
1:FRAMES 3:MEMBERS
2:FRAME-BAY 4:MEMBER-PORTION 6:PARAMETERS
5:MEMBER-SECTION RTN:RETURN
1 **
FACTORS
& PARAMETERS
COMPATABILITY
OF
FOR
ALL
BAYS
OF
- s e l e c t d e t a i l s of c h e c k s on f r a m e s showing failures
FRAME
PARTS DATUM DATUM DATUM DATUM DATUM DATUM DATUM DATUM DATUM
1 2 3 4 5 6 7 8 9
2 3 5 5 6 8 8 - 10 - 10
OK OK OK OK OK OK OK OK OK
Figure 6(d). Sample display during design of a multi-bay portal frame with lean-to They may be selected by frame, bay, members, portion of member or cross section. Comments indicate when a
volume 17 number 2 march 1985
relevant check is, in fact, inapplicable. After a command requesting display, and before presentation of fresh design
91
INTEGRITY SNAP-SWAY
CHECKS
BAY
FOR
BAY
FAILS
FUNCTIONAL
** F A C T O R S
:
45.5
/ 30.5
: (SPAN/RD)/FY
1.49
:
45.5
/ 30.5
: (SPAN/RD)/FY
FAILS
PERFORMANCE
T O P OF S T A N C H I O N : N O D E
PERF
: DEFL(M)
/ PERM DEFL(M)
2 5 8
0.22 0.01 0.23
: -0.006 : 0.000 : 0.006
/ / /
MIDSPAN:NODE
PERF
: DEFL(M)
/ PERM DEFL(M)
3 6
0.89 0.86
: :
/ /
ROOF
*SELECT
1.49 2
SWAY
IN C H E C K
*SELECT
FRAME
i SWAY
*PAUSE
PORTAL
v a l u e s of indicator and parameters
0.020 0.020
2:FRAME-BAY 4:MEMBER-PORTION 5:MEMBER-SECTION 6:PARAMETERS RTN:RETURN
NUMBER
& PARAMETERS
COMPATABILITY
-
RESULTS
I:FRAMES 3:MEMBERS
MEMBER
-0.018 -0.017
0.027 0.027 0.027
- select further detailed results
4 FOR M~4BER
4 -
5
OF P A R T S DATUM
4 -
5
OK
INTEGRITY
-
MEMBER PO
*LTBX
OK
* CAXM
FALLS
full d e t a i l s of all i n d i c a t o r s and parameters
1 : MOMENTS
PO
REVERSE
OVER
PORTION
i RPM
0.88 0.55 0.23
: : :
176.6 / 200.0 : L A M D A X / S R 0.001*AY*(LAMDAX-LAMDXO) 54.6 / 240.0 : P C X / P Y
0.36 0.ii 0.82 1.22 0.01
: : : : :
0.01
•
X: 1003.? Y: 175.6 72.7 / 200.0 : LAMDAY/SR 0.001*AY*(LAMDAY-LAMDYO) 196.4 / 240.0 : PCY/PY O.OO7*(LAMDL-LAMDE) 0.5 / 240.9 : M Y / M C Y
MEMBER * SHRY *PAUSE
IN C H E C K
*PAUSE
IN O U T P U T
OK -0.1 /
631.9
: QY/PQ
RESULTS
COSTS
FOR S T R U C T U R E
- list of e s t i m a t e d costs
PART DATUM
i -
2
DATUM
2 -
3
MEMBER
384.15
MEMBER HAUNCH
179.30 64.84 - console omitted
DATUM
8 -
i0
DATUM
9 -
i0
TOTAL
MEMBER
49.90
MEMBER
977.93
ESTIMATE =
*PAUSE
IN O U T P U T
*PAUSE
IN T A S K
display in f i g u r e
2273.71
- design
continues
Figure 6(e). Sample display during design of a multi-bay portal frame with lean-to 92
computer-aided design
information, the screen is cleared and the cursor is moved to the top left hand corner. Redundant information is rapidly replaced by that currently selected. At the end of each operation the program pauses awaiting immediate selection of a further design option. Relevant options following a particular display of results are presented in a manner that emphasises the designer's control of the computer. Revision of the structural arrangement is eased by convenient selective perusal of the wide range of design check information available.
CONCLUSIONS Consideration of the design process suggests that an effective aid to design decision-making must provide for scrutiny of relevant performance indicators related to design checks. Also, information describing the detailed basis of design checks should be readily available to the designer, preferably as part of the software. A computer design aid has been described which provides assistance in the selection and assessmentof structural arrangements for steel frameworks. A particular technique has been devised to integrate the tasks of handling design selection and assessmentinto one computerized aid. This technique enables virtually any design check, including cost, to be incorporated in a consistent manner. The effectiveness of the computer aid stems from the facilities provided both to alter and scrutinize a database describing structural layout, loading and performance, together with the ability to select and organize a large number of relevant design checks. To this end, a convenient basis for selective review of design options and information has been devised. A modular program structure permits ready incorporation of additional design checks for a variety of structural elements. Also the checks may be devised to suit individual preferences of the designer. Virtually all limit states can be checked systematically using a computing aid of the type described. Information to determine applicable checks need not be generated manually by the designer. Selecting checks for a structure is replaced by specifying the type of structure to be designed. Reduction in the amount of data to be communicated leads to considerable saving in design time and effort. Arrangements of design data not readily generated by other types of program may be displayed in rapid succession to assist decision making, following the single global check on performance. In particular, performance indicators, together with costs, may be compared for all design checks carried out. For a given design, display of selected check
volume 17 number 2 march 1985
results is virtually instantaneous. Computational delay occurs only during routine generation of initial designs from concise input data or during the brief phase in which all checks are systematically carried out for the defined design. The program offers a viable and much more powerful alternative to packages based essentially on manual design methods. For effective use, each designer would require constant and convenient accessto such a facility. The improved potential of small computers should allow this requirement to be met in the near future.
ACKNOWLEDGEMENTS Work related to this paper was carried out in the course of a SERC Total Technology scheme of study at the Department of Civil Engineering, University of Leeds. Views on current and future needs relating to CAD in structural steelwork were gratefully received from member firms and technical staff of the British Constructional Steelwor'k Association.
REFERENCES 1 Beeby, A W'Reinforced concrete design calculations using small computers - DECIDE' 5truct. Eng. Vol 56A No 10 (October 1978) pp 287-289 2 Yeadon, R E 'The interactive design of portal framed buildings' Struct. Eng. Vol 57A No 9 (September 1979) pp 288-292 3 Laxon, W R, Malby, K H, Mounfford, D H and Shuttleworth, B T 'Automatic design of structural steelwork' Comput.-Aided Des. Vol 12 No 1 (January 1980) pp 35-42 4 Morris, L J and Randell, A L Plastic Design Constrado (1975)
5 Croft, D D 'The GLADYS computer system for the design of reinforced concrete elements' 5truct. Eng. Vol 56A No 10 (October 1978) pp 282-286 6 Moore, M G and Brotton, D M 'Interactive design and detailing of structural steelwork connections using a computer' 5truct. Eng. Vol 52 No 4 (April 1974) pp 133-142 7 British Standards Institution Draft standard specification for the structural use o f steelwork in buildings BSI London (1977) also Section 12 and associated appendices BSI London (1979)
93