Wednesday, September 20, 2017

Emulation for optimal structural design.

Emulation for optimal structural design.

 

If you are fond to ancient world engineering and the surprising achievements of the humanity such as the  Pyramid of Egypt, you will notice that the Pharaohs of the ancient empire  had to perform some failed attempts before they could build the Giza Pyramids Complex. After the famous engineer, architect and erudite Imhotep built the  stepped Saqqara pyramid, of seventy meters high, the precedent Pharaohs attempted the construction of next level pyramids.

But the next attempt, the Medium pyramid, ended up collapsing under its own weight, while the next one, the Dahshir pyramid, had to suddenly change its angle, since the collapse of its internal structure seemed to be unavoidable.

We had to wait until the Red Pyramid at short distance from the previous one, for achieving the adequate resting angle for obtaining the proper structural integrity.
Red Pyramid
Thousands of years later, during the XIX century when the railroad network extended to all the corners of the industrialized countries Great Britain and  United States, as the leaders, the need of saving chasms and rivers, fomented the construction of bridges.

Not everybody was successful, Stirling, Broughton, Chester, Wooton, Tay in Scotland and Inerythan, were example of this delirious and tragic beginning of the structural engineering in the United Kingdom of the industrial revolution.

North America, also had its named failures, some already during the 20th century and several filmed as classic catastrophes movies.

All these structural failures that costed dozens of deaths and wounded helped as experience so we can now enjoy of safer structures, but  not quite still.

Even so this doesn't mean we  no longer have structural failure. New needs present new challenges. The frail for urban space leads to the constriction of structures simultaneously higher and deeper, where the deep excavations incidents present themselves at an alarming rate.

Here is where structural analysis software such as Autodesk Robot Structural permits us design structures and test them before wind or seismic load cases that may be catastrophic. Including big frames structures subjected to accidental loads.
Accidental Loads
This doesn't mean though that we should design thinking always on the catastrophes. Actually there's regulations and design codes regarding the cases that should be considered. The safety coefficients that should be respected and the accidental load cases that must be included.

In more practical cases, Autodesk RSA permits us to try different structural proposals without more work than changing  the beams and columns section selection.

It's not unusual, that our first structural proposal happens to be somehow oversized. We all design with certain degree of fear that our design calculations present some error or that our sections cant bear the loads. Furthermore, that the design loads won't be respected and that the structure get overloaded. It's something rather common.

Autodesk Robot Structural allows us to observe the deformations in the structure in a graphic way before all the different load cases and combinations. The structure deforms affected by the a certain scale, so we can further appreciate each load effect.

From there we could verify the shear and bending moment graphs, but the most evident aspect is observing the deformations as we check each section.
Structural Deformations
With this information we can test different sections until we get to a solution that offer us the best relation between safety and economy.

It's easy to switch structural elements of steel or reinforced concrete and observe the deformations and critical points.

Before the same set of load cases combinations we can check different steel and concrete elements, observing the results through deformation that may be animated, but that will throw the results in a way of a color code and precise values over the deformation points.
Since we can determine the deformation scale, is quite easy to appreciate how the stresses are exerted over the structure.

From these first results and the real-time displayed safety coefficients it's possible to switch structural elements for slimmer or lighter members and observe the deformation and coefficient changes.

The simulation can be taken to a critical point and from there test members, connections or far more creative geometry elements that resolve the transfer of weight and stresses in a more clever way,so we can obtain lighter and more resistant structures.

As oppose to other calculation programs where the changes in the structure involves a long process of mathematical rethinking, in Autodesk Robot Structural such process is graphical making the analyst feel motivated to perform a bigger amount of changes y tests, as if it was some sort of virtual construction game.

The effects of each change in the structure are also displayed in a graphical way, being possible to work with complete combinations involving wind, seismic and accidental loads, including any other event to which the structure could be subjected along with its respective foundation.

published by Virginia E-Learning.

Thursday, September 14, 2017

Autodesk Robot Structural and the Ground Anchors.

Autodesk Robot Structural and the Ground Anchors.

 

In fact, Autodesk RSA is not a specif application for the designing of ground anchors.
But their tools for evaluating ground loads can be extremely useful in the work of designing a ground anchors containment system.
Retaining Walls
Knowing this thrust necessary before you can make the decision on which is the most appropriate containment system and make the decision between shoot crate walls, steel mesh reinforcement, solider beam and lagging or a big reinforcement concrete containment wall.

In this document, we will make a comparison between the land loads thrown by Autodesk Robot Structural analysis and those obtained by the diagram of apparent pressure of the land used by the Federal Administration of roads of the Department of transportation of United States (FHWA), which are employed by the AASHTO.

Let's observe that FHWA-AASHTO uste the method of apparent envelope of the ground pressures of Terzaghi and Peck, in terms that Autodesk RSA uses a method of increasing the thrust of the soil in proportion to the depth of the excavation, the geothecnical profile, K coefficient, groundwater level and the nearest structures weights.
Robot Structural 2018 Walls
None is wrong about the other. They are two approaches to the same problem. And both solutions coincide in the middle of the graph and the general maintain approximate values for the same ground conditions. In any way exists a coefficient of the uncertainty in relation to the soil loads called K.

This allow us to take Autodesk Robot Structural as a reliable tool for quickly getting the load value of the land within a range of acceptable values.
To emulate this containment screen supported by ground anchors, we have sketched in Autodesk RSA an element of reinforced concrete composed by walls based on two-directions slabs.

From these interceptions depart tensors into a virtual land, that is ten meters deep, sustained by elastic supports with a certain coefficient of ballast, calculated by the geothecnical Robot's calculator.

The conditions for the volumetric weight, friction angle and overload of the traffic are the same from the example. However, note that the geometry of the envelope in Autodesk RSA  load differs from the one considered by the Terzaghi and Peck for the diagram of apparent pressure from the soil.

We cannot say that is wrong, but it should be noted that both methods applied to the tributary area, as is is in the joint area, part from steel elements driven deep into the suitable land that is help by anchors to specified levels.
Ground AnchorsRobot Structural specifically calculates the load of the soil at rest, pressing on a screen. We conclude that the values are not significantly different and can be taken as a first exploratory data or approach, for which we could quickly establish criteria for possible alternative solutions.

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