Fourteen storeys of a concrete frame curved in plan, a block twelve bays long that follows 150° of a ring 30 m from its middle, two bays of 7.5 m deep, with a 220 mm slab at every floor. The El Centro earthquake shakes the ground along x, across its middle.
The first 20 s of El Centro, as they happened, the movement drawn larger than it is. Beside it, the ground's acceleration and the movement along x of a tip of the roof, over the same 20 s.
The model
| Group | What it does |
|---|---|
| 1 - Geometry | The sliders - Bays along it, Bays deep, Bay, Inner radius, Sweep, Storeys and Storey height - and a Python component that draws the frame from them: its grid bent round the ring, the beams cut twice a bay and following its curve, a slab mesh at every floor, the columns' feet, and a tip of the roof the charts follow. |
| 2 - Members | Concrete C30/37 from Material Library; columns 0.7 × 0.7 m and beams 0.4 × 0.7 m, RectangleCS sections, as ForceBeamColumn; 220 mm of concrete, a Plate Fiber Section, as ASD Shells. |
| 3 - Supports | Every column built in at the ground, with a Support. |
| 4 - Ground motion | The El Centro record from a Python component, its first Duration seconds times Ground motion scale; a Path Time Series of it; a Load Pattern of the UniformExcitation type, along the direction it shakes. |
| 5 - Transient analysis | Assemble, with an MPCO Recorder of the displacements alone, which is all the view reads; Damping, Rayleigh's from Damping and its two frequencies; the Newmark Integrator; Analysis Step, a step a sample of the record; Analysis Settings for a transient analysis with the Linear algorithm, one solve a step, as an elastic model needs; and Run Analysis. |
| 6 - Results | A Model View of the analysed model at Step, deformed 25 times, its elements' edges and its supports drawn, its colours in iso-surfaces on the slabs over 0 to 200 mm for every step alike, with a Legend. Drag Step to go through the record. |
Its 3 600 elements are past the free limit of 50: it needs a licence. The analysis takes about three minutes on a laptop; then each step takes a second or a few to draw as you drag Step.
The ground motion
El Centro, 18 May 1940, the north-south component: 0.32 g at its peak, 2 s in, the first 20 s of it. A Path Time Series of its accelerations shakes the ground under the whole structure through a Load Pattern's UniformExcitation type, and Run Analysis follows it step by step, 0.02 s at a time, a transient analysis with Newmark's average acceleration. Damping is Rayleigh's, 5% of critical at two frequencies that bracket the modes that matter. Ground motion scale makes the record stronger or weaker, Duration takes more or less of it.
What it shows
The block sways along x almost as one, its floors tied together by their slabs: the tips of its roof move 168 mm at the most, 6.2 s in, and the middle of its outer face 3% less. Its first three periods come close together, at 1.6 s, 1.6 s and 1.5 s.
The moment it moves the most, and the record up to then.
Try
- Sweep at 270: nearly a ring.
- Bays deep at 3: a deeper block, stiffer across.
- Shake it along y, across the other way: type Y into the ground motion's Load Pattern.
