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12 votes
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How can large bridges be made resistant to earthquakes?

You can never make something earthquake proof, but there are many things that can be done to resist earthquakes. There are long-span bridges built in earthquake zones. For example, the Akashi Kaikyo ...
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10 votes
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Why are tremors of an earthquake felt more on upper floors?

First, your statement is not universally true. Motion of the bottom of a building can be greater or lesser in upper floors. It depends on the type of motion, how free the building is to move in ...
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8 votes

What drives improvements in seismic safety?

This is a pretty huge topic, but I can summarize a couple major factors. More population, more damage, more awareness The effect of a disaster that kills thousands of people and causes property ...
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7 votes
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How to derive Equivalent Static Load for irregular structure modeled with FEM?

The short answer to your question, How can we compute the Equivalent Static Lateral Forces, the overturning moment and other quantities in an irregular building/structural discretized by finite ...
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6 votes

Why are tremors of an earthquake felt more on upper floors?

Harmonic coupling with the building's natural vibration frequencies, dissipation of energy in a massive building, and the variety of vibration modes that can experience coupling could result in more ...
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6 votes

Accidental Torsion and Equivalent Static Load for an irregular structure

How should we obtain $F_x$, given that it is lateral static force, but we are doing dynamic analysis? $F_x$ is the sum of the lateral force for a story. If you've performed a dynamic analysis, ...
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5 votes

How can large bridges be made resistant to earthquakes?

Actually very long bridges (and super-tall buildings) often have less issues with earthquakes than their smaller brethren. This is due to them generally being much more flexible and therefore having ...
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4 votes

What is the frequncy range of seismic vibrations?

The frequency and ground acceleration and other pertinent data are recorded in a seismic design espectra which is unique for each site and varies with the type of the soil on the side. Usually ...
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3 votes
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Would a larger building more safely or smoothly ride the seismic waves of an earthquake?

Earthquake waves are very long. For example in California, the frequency of the 1996 Northridge earthquake was 0.5Hertz. This shock could cross the diameter of the earth in half an hour (Not correct! ...
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2 votes
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How to calculate the relative contribution of each mode in seismic dynamic mode analysis?

You should be normalizing your eigenvector so that the generalized mass matrix (defined by $ \hat{m} = \phi^T M \phi$) is the identity matrix, and therefore, the generalized mass of the rth mode (...
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2 votes

How can large bridges be made resistant to earthquakes?

I am going to center in one of the most famous bridges of these conditions last years: San Francisco Bay Bridge. This bridge is not planned for trains, and so they tested with huge hydraulic jacks (...
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  • 181
2 votes

Would a larger building more safely or smoothly ride the seismic waves of an earthquake?

If a large ship is hit side on by a huge it can roll over. Ships have better success at surviving large waves by sailing into large waves. Size of buildings is one factor. How it is built is another ...
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2 votes

Seismic question

The one with the higher mass on level three is worse. Assuming the building as an SDF vibration for simplicity: The period of the building will moderately increase due to the reduction of K, $$K=P/\...
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2 votes

Generating a Blank Seismic Tripartite Graph

This is the only place on the internet that I could find that actually gave decent resolution images for tripartite plotting paper. However, it had some limits that affected use in our area: 1) the ...
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2 votes
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Generating a Blank Seismic Tripartite Graph

You can try running the following R script which produces the figure below. ...
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2 votes
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Why is it useful to scale seismic ground motion data

A ground motion record (accelerogram) is a measurement with high specificity to the fault that caused the earthquake. The recorded peak acceleration, frequencies, duration etc depend on the fault ...
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1 vote

Wind load vs Earthquake load and R factor

Increasing the R factor decreases the load that the building has to resist during an earthquake. Any easy example of this is a wood building. The cheapest choice for wood shear wall sheathing would ...
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  • 266
1 vote

Slab Stiffness Modifiers applied in Vertical Elements design but not in Slab design?

If you read the commentary of the ACI code you you will understand that stiffness modifiers take into account the cracked section properties expected from cyclical loading. Slabs / diaphragms are a ...
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1 vote
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How to distribute moment from Lateral Load Method (Static Analysis IBC for example) to Each shear wall individually?

Your question seems like it is incomplete so it's difficult to provide a complete answer. For the moment computation, what you'll need to do is compute the centroid of rotational stiffness, which is ...
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1 vote

How to handle modal combination in response spectrum analysis for member forces for member with more than 1 element?

You are correct that the response for each mode must be calculated before applying some modal combination methodology. Instead of thinking about the structure as being discretized into numerous ...
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