Fitzroy Systems

Software for Structural Engineers

NL-STRESS *** Non Linear STRuctural Engineering System Solver ***

NL-STRESS is a computer program for elastic and non linear (plastic and stability) analysis of skeletal structures.

A full version is supplied as part of SCALE together with several 'data generators' including the GUI (Graphical User Interface) which permits the engineer to draw the structure to be analysed on the screen. Each data generator builds a data file (.DAT) which contains page headings for the results file followed by: joint coordinates, member incidences, loading and other data.

NL-STRESS results are in calc-sheet format supported by 2D/3D plots of bending moments, shear forces or deflections on the screen or printer. Results may be restricted to a selection of members and/or joints.

The form of data required by NL-STRESS is the same as that for the well-known program called STRESS, developed at the Massachusetts Institute of Technology in the early 1960s. But in NL-STRESS there are additional keywords for dealing with non-linearity - a subject not catered for in STRESS. There are also novel facilities in NL-STRESS for generating sequences of data automatically. Although it is over 40 years since the MIT STRESS program was developed, keywords such as: JOINT COORDINATES, MEMBER INCIDENCES, JOINT LOADS, MEMBER LOADS are as applicable today as they were then. It makes little sense to change them just for the sake of change. What has changed is the program itself; not a single line of data in NL-STRESS has been taken from MIT STRESS. NL-STRESS has Department of Transport approval reference MOT/EBP/254C.

NL-STRESS Proforma Data Files.

NL-STRESS proforma data files are text files for frequently occurring problems. The engineer has only to nominate the proforma data file, and use the editor in NL-STRESS to set the parameters (spans and loading etc.), joint coordinates and other data being computed automatically. Over 150 proforma data files are provided, a summary follows:

cb01-cb14.ndf Continuous beams single span to 14 spans with UDLs
cbp01-cbp14.ndf with UDLs and concentrated loads (other loading may be added).
ms1x1-ms5x5.ndf Single storey one bay and 1 storey up to five bays and five multi-storey frames.
ng02-ng08.ndf N girders 2-8 bays.
nls.ndf Proforma for 'one off' frames e.g. a 3000 joint space frame.
port1-port4.ndf One to four bay portal frames without haunches.
port1h-port4h.ndf One to four bay portal frames with haunches.
port2h1-port4h1.ndf Two to four bay portal frames with haunches and a single ridge.

Roof trusses:
rtattic.ndf Attic room
rtcolar.ndf Collar-tie
rtcolat.ndf Collar-and-tie
rtcolats.ndf Collar-and-sloping tie
rtcoup.ndf Couple
rtcoupc.ndf Couple close
rtfink.ndf Fink
rtking.ndf King post
rtmans.ndf Mansard - steel
rtmant.ndf Mansard - timber
rtqueen.ndf Queen post
sub01-sub08.ndf Subframes from one to eight bays.
subh01-subh08.ndf Half subframes from one to eight bays.
wg02-wg08.ndf Warren girders from two to eight bays.

Simple Changes.

Engineers analyse a frame many times experimenting with changes to the section properties, support conditions etc.; it is important therefore that changing the data be simple. No matter which method of data preparation is used (including drawing the structure on the screen using the GUI), a text file of data is created written in the NL-STRESS language. The engineer may use his/her favourite editor to change the data, or run NL-STRESS and use the simple editor incorporated into the program.

Stability Analysis.

Prepare the data as for elastic analysis and give the commands 'METHOD SWAY' and 'NUMBER OF SEGMENTS 6' and 'NUMBER OF INCREMENTS 20'; where the 6 tells the program to divide each member into six segments, and the 20 tells the program to apply the loading in 20 increments. (If the structure is triangulated with loading applied only at the joints then it will also be necessary to provide an initial bow to each member to induce buckling, and this may be done by including a percentage e.g. 0.1 following the number of segments.) Guyed masts and other tension structures can be handled by METHOD SWAY, worked examples are provided.

Plastic Analysis.

It is simple to find the collapse load factor for any frame which has been analysed elastically, by changing METHOD ELASTIC to METHOD PLASTIC, giving NUMBER OF INCREMENTS 40, doubling the working load, and giving the yield stress following the constants command. If the analysis reports collapse after say 36 increments then the collapse load factor is 36/(40/2)=1.8 (assuming the working load has been doubled).

When section properties are specified by shape (e.g. ISECTION) and dimensions, NL-STRESS computes plastic section properties automatically, and applies the appropriate interaction formulae for the shape, thus saving the engineer much time. False mechanisms are prevented, 'unloaded' plastic hinges are recognised and taken into account.

Additional Features.

Members may have springs at their ends; and any member may be specified as 'tension only' or 'compression only'. NL-STRESS will compute elastic stresses.

SCALE supports batch processing of Windows programs, thus several analyses of large frames may be run overnight by NL-STRESS.

The keyword COLLECTION causes the displacements for all loadcases for each joint to be collected and printed as a group; similarly for member forces, member stresses and support reactions.

The keyword DIAGRAMS also collects the results of all loadcases together for each member but presents the information as a diagram showing the bending moment and shear force envelopes.

The keyword AREA tells NL-STRESS to spread a load over an area of a grid. The keyword SUMMARY makes NL-STRESS print a summary of joint, member and loading data.

LOADING DYNAMIC <g>, where <g> is the acceleration due to gravity e.g. 9.80665 m/sec2, tells NL-STRESS that the loading case is to be treated as a dynamic loading and the natural frequency computed by energy methods.

NL-STRESS Benchmarks.

NL-STRESS benchmarks are examples of data files, which cover a wide range of engineering structures. Embedded in the data will be found part of the results of an NL-STRESS analysis so that the problem may be run and the results obtained compared to those embedded in the data; therefore the set of data files may be used as benchmarks against which the results obtained from running the problem on a computer can be compared. Any technical references are given in the benchmark examples. The filename extension is given as .BMK (short for BenchMarK) to distinguish the files from other NL-STRESS data files. To get pictures of the benchmark examples, run NL-STRESS.

Timing Benchmarks.

bm01.bmk Plane frame with 27 joints, 38 members & 2 load cases
bm02.bmk Space frame with 66 joints, 99 members & 1 load case

Department Of Transport - HECB Calibration Test Benchmarks.

dt01.bmk Plane truss with varying relative stiffness
dt02.bmk Plane frame with displaced supports
dt03.bmk Plane frame problem (2)
dt04.bmk Encastre segmental arch rib
dt05.bmk Grillage with applied displacements & elastic supports
dt06.bmk Grillage with shear deformation
dt07.bmk Skew deck of orthogonal grillage
dt08.bmk Circular-arc bow girder
dt09.bmk Space truss
dt10.bmk Space frame with varying stiffnesses & displaced supports

Dynamical Behaviour Benchmarks.

dy01.bmk Ex. from Fig 3.2 from Dynamical Behaviour of Stuctures
dy02.bmk Ex. from Table 12.2 in Steel Designers' Manual
dy03.bmk Ex. from Table 12.2 in Steel Designers' Manual
dy04.bmk Nat. freq of beam with point loads, Dunkerley's method
dy05.bmk Nat. freq example 10.3-2 by Coates, Coutie & Kong
dy06.bmk Nat. freq example in Fig 4.8 by GB Warburton
dy07.bmk Nat. freq example problem 1 in Chapter 1 by Warburton
dy08.bmk Nat. freq example problem 7 in Chapter 15 by Ryder
dy09.bmk Nat. freq grid problem cl.12.15 Steel Designers' Manual

Plane Grid Benchmarks.

gr01.bmk Bridge deck from C&CA manual
gr02.bmk Foundation raft
gr03.bmk Authentic bridge deck
gr04.bmk Curved balcony member from Design Ex. 6 BC842 by SCI.
gr05.bmk Member stresses for sections defined by props or geometry

Plane Frame Benchmarks.

pf01.bmk Shear wall
pf02.bmk Box culvert
pf03.bmk Influence lines
pf04.bmk Natural frequency determination
pf05.bmk Prestressed continuous beam
pf06.bmk Shear deformation - Ex. 6.7-1 by Coates Coutie & Kong
pf07.bmk Member loads - Example 6.7-2 by Coates Coutie & Kong
pf08.bmk Symmetry - Example 6.10-1 by Coates Coutie & Kong
pf09.bmk REPEAT-UNTIL-ENDREPEAT - Problem 6.1 by Coates et al.
pf10.bmk Looping across tables - Pr. 6.2 Coates Coutie & Kong
pf11.bmk Springs at supports - Pr. 7.18 by Coates Coutie & Kong
pf12.bmk Applied moments - Problem 8.5 by Coates Coutie & Kong
pf13.bmk DIAGRAMS example - Pr. 6.14 by Coates Coutie & Kong
pf14.bmk Propping force - Problem 6.16 by Coates Coutie & Kong
pf15.bmk Member distortions - Pr. 4.15 by Coates Coutie & Kong
pf16.bmk Temperature, self weights, length coefficients example
pf17.bmk Curved member, Design example 6 Job BCC 842 by SCI
pf18.bmk Temperature gradient, ex. from GIT-ICES STRUDL-II manual
pf19.bmk Stresses for sections defined by properties or geometry
pf20.bmk Member properties given by: AS other member properties

Plastic Analysis Benchmarks.

pl01.bmk Single bay portal frame
pl02.bmk Two storey frame
pl03.bmk Plastic grillage
pl04.bmk Elastic-plastic analysis of compression members
pl05.bmk Reversing plastic hinge example
pl06.bmk Example 1.1 from Constrado publication 'Plastic Design'
pl07.bmk Example 1.2 from 'Plastic Design'
pl08.bmk Example 2.1 from 'Plastic Design'
pl09.bmk Example 2.3 from 'Plastic Design'
pl10.bmk Example 4.4 from 'Plastic Design'
pl11.bmk Example 4.7 from 'Plastic Design'
pl12.bmk Example 6.2 from 'Plastic Design'
pl13.bmk Test order of formation of plastic hinges
pl14.bmk Portal frame with out of plane loading
pl15.bmk Space frame - ring beam supported on RHS columns
pl16.bmk Example 14.6-1 from Coates Coutie and Kong
pl17.bmk Example 14.6-4 from Coates Coutie and Kong
pl18.bmk Example 14.6-5 from Coates Coutie and Kong
pl19.bmk Example 14.7-1 from Coates Coutie and Kong
pl20.bmk Example 14.7-2 from Coates Coutie and Kong
pl21.bmk Example 14.8-1 from Coates Coutie and Kong

Plane Truss Benchmarks.

pt01.bmk Computer Methods in Solid Mech. by Gennaro: Example 20
pt02.bmk Computer Methods in Solid Mech. by Gennaro: Example 22
pt03.bmk Computer Methods in Solid Mech. Chapter 4 Problem 1
pt04.bmk Computer Methods in Solid Mech. Chapter 4 Problem 4
pt05.bmk Computer Methods in Solid Mech. Chapter 4 Problem 13
pt06.bmk Computer Methods in Solid Mech. by Gennaro: Example 31
pt07.bmk Computer Methods in Solid Mech. by Gennaro: Example 32
pt08.bmk Computer Methods in Solid Mech. by Gennaro: Example 33
pt09.bmk Computer Methods in Solid Mech. by Gennaro: Example 34
pt10.bmk Analysis of Indeterminate Structures Grassie: Ex. 4.10

Space Frame Benchmarks.

sf01.bmk Cantilever stair
sf02.bmk Guide dolphin
sf03.bmk Example in Fig 3-8 from William Weaver
sf04.bmk Example in Fig 3-9 from William Weaver
sf05.bmk Example from UCC symposium Nov 1972
sf06.bmk Tapered beams example - equivalent to rect. section
sf07.bmk Cant. beam subjected to standard loadings from S.D.M.
sf08.bmk S.S. beam subjected to standard loadings from S.D.M.
sf09.bmk Built-in beam subject to standard loadings from S.D.M.
sf10.bmk Ring beam on T columns to show need for BETA angle
sf11.bmk Curved balcony member for SCI design example 6
sf13.bmk Member distortions for cantilever or built-in beam
sf14.bmk Temperature gradient, ex. from GIT-ICES STRUDL-II manual
sf15.bmk Stresses for sections defined by properties or geometry

Sway Frame Benchmarks.

sw01.bmk Column with axial load (Euler buckling problem)
sw02.bmk Column with axial load and lateral load
sw03.bmk Guyed mast analysis
sw04.bmk Two storey frame
sw05.bmk Lateral displacement of tip of end loaded cantilever
sw06.bmk Suspension bridge with three pinned stiffening girder
sw07.bmk Comparison between member end springs & pseudo springs
sw08.bmk Modelling imperfections by parabolic bow
sw09.bmk Example 9.11-1 from Coates Coutie & Kong
sw10.bmk Problem 9.1 from Coates Coutie & Kong
sw11.bmk Problem 9.2 from Coates Coutie & Kong
sw12.bmk Problem 9.8 from Coates Coutie & Kong
sw13.bmk Problem 9.9 from Coates Coutie & Kong
sw14.bmk Problem 9.10 from Coates Coutie & Kong
sw15.bmk Problem 9.11 from Coates Coutie & Kong
sw16.bmk Problem 9.12 from Coates Coutie & Kong
sw17.bmk Two way net subjected to symmetrical loading
sw18.bmk Two way net subjected to unsymmetrical loading
sw19.bmk Hyperbolic paraboloid net
sw20.bmk Stable and unstable post-buckling behaviour
sw21.bmk Snap through - Problem 9.8-1 from Coates Coutie & Kong