3D frames and trusses
Nodes, members, releases and supports in tables, with the structure beside them. Steel shapes, concrete rectangles or your own section properties.
Analysis and design of structures
Model a frame in three dimensions, analyse it under static and seismic loads, and design its steel and concrete members, slabs and footings by NSCP 2015. One desktop app, with every number's calculation a click away.
What it does
From the model to the bar schedule, in four tabs: Model, Results, Dynamics, Design.
Static analysis, and P-Δ
Every load case and combination: deflected shapes, reactions, and diagrams of N, Vy, Vz, T, My and Mz. Combinations can be taken to second order.
Dynamics
Natural modes you can set swinging, the response spectrum method with CQC or SRSS, and the response over time to a ground motion record.
Seismic loads by the Code
The NSCP 2015 design spectrum from Ca and Cv, the static force procedure of Section 208.5.2, and the spectrum scaled to its base shear.
Steel design
NSCP 2015 Chapter 5 (AISC 360-10), LRFD or ASD: tension, compression, bending, shear and their interaction, and the lightest shape that works.
Concrete design
NSCP 2015 Chapter 4 (ACI 318-14): beam bars and stirrups, and column bars from the biaxial interaction surface, with slenderness.
Slabs
Flat panels analysed as plates by finite elements. They put their loads on the beams around them, and get their bars each way.
Footings
An isolated footing under every support: sized for the soil's allowable pressure, then designed for shear and bending.
Load combinations
Generated from NSCP 2015 Section 203 for LRFD or ASD, from the kinds of your load cases. Edit any factor.
A tour
1
Model
Fill in the tables, or start from a frame of so many bays and storeys. Loads go on nodes, members and slabs, and show on the structure as you enter them.
2
Results
Pick a case or a combination and a diagram. Click a member for its forces along its length, or a slab for a map of its deflection and moments.
3
Dynamics
Periods, frequencies and the mass each mode carries. The spectrum and static seismic cases join the combinations with one click.
4
Design
Every member coloured by demand over strength. Click one and read the calculation: the strengths, the governing combination, the bars.
5
Foundations
Footings drawn in plan under their columns, each with its size, thickness, bars and the checks behind them.
Examples to start from
The Examples menu opens ready-made structures. Some can be checked by hand.
- Simply supported steel beam wL²/8 at midspan, to the digit.
- Continuous concrete beam Top bars over the supports, bottom bars in the spans.
- Steel portal frame Dead, live and wind on pinned feet.
- Pratt truss Chords and diagonals in tension and compression.
- Slab on four beams A plate, its beams, columns and footings.
- Concrete building with slabs Static seismic forces and a scaled spectrum.
- Steel frame with P-Δ Four storeys, to second order.
- Tower under ground motion Resonance, cycle by cycle.
What it doesn't do
An engineer should know where a tool stops. Girder says so in its guide, and here.
- Slabs load the frame but don't stiffen it: there are no rigid diaphragms, walls or shells.
- Members are straight and prismatic, without shear deformation.
- Steel shapes are wide flanges, rectangular hollow sections and pipes. Their properties come from their dimensions without fillets, a few percent below the tabulated values.
- Concrete sections are rectangles. Torsion design, seismic detailing (Section 418) and long-term deflections aren't covered.
- Footings are isolated, square and concentric: no combined footings, mats or piles.
- Accidental torsion, the redundancy factor ρ and Ω₀ aren't applied to the seismic cases.
Girder is an aid to an engineer's judgment. Check its results against your own before building on them.
Download
Girder runs on macOS, with Windows to follow.