How do structures carry wind and seismic loads? An Intro to Lateral Force Resisting Systems
Buildings carry lateral (i.e., horizontal) loads through lateral force resisting systems. This video introduces the three most common systems: (1) Braced frames (2) Moment frames (3) Shear walls
The lateral force resisting system does not need to cover the entire structural system, but lateral loads do need to be able to transfer from their point of application to the LFRS.
This tutorial adds material plasticity into nonlinear analysis, illustrating this behavior in a steel coupon tested in tension.
Learning objectives:
1. Define bilinear and multilinear plasticity properties.
2. Apply symmetry constraints to reduce the size of the model.
3. Describe the phenomenon of necking and why it occurs for plastic materials.
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https://www.youtube.com/watch?v=9wF2Yp2Y4-s
This video defines determinate and indeterminate structural systems, and how to tell the difference.
The unknown reaction forces and internal forces of determinate systems can be solved using only the equations of equilibrium (i.e., statics). Indeterminate systems have more unknowns than can be solved using statics alone, and therefore new structural analysis techniques are required.
The number of unknowns can be counted and compared to the number of equilibrium equations. Examples are shown for how to do this with trusses and frames (or beams, which work the same as frames).
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https://www.youtube.com/watch?v=ml26FjTl-C8
This video is the first in a series on approximate structural analysis. Approximate analysis is valuable for checking results from an indeterminate or computer analysis. It is also very useful for multiple choice exams, such as the FE and PE exams - getting a quick answer that is close enough can eliminate incorrect solutions or even hone in on the correct answer.
This first video focuses on indeterminate beam analysis. An indeterminate system is converted to a determinate system by adding hinges at the inflection points (i.e., the locations of zero moment). Principles of locating inflection points are discussed, and two full examples problems are shown.
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https://www.youtube.com/watch?v=hkLWq9eD4pk
Shear capacity of reinforced concrete beams has changed from ACI 318-14 to the latest code edition, ACI 318-19. The detailed method is no more, and significant changes have been made the concrete term Vc.
This video gives an overview of shear in reinforced concrete beams, highlights the changes in the concrete Vc term, and reviews the steel stirrup contribution Vs. Two example problems are completed: the first for a beam with less than minimum transverse reinforcement, and the second for a beam with more than the minimum transverse reinforcement.
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Chapters:
0:00 Introduction
2:40 Concrete Vc
6:08 Steel Vs
7:57 Example 1
11:31 Example 2
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https://www.youtube.com/watch?v=qeAI_zYx6gA
This tutorial models a concrete beam reinforced with mild steel. The concrete is modeled using a Menetrey-Willam strain softening model, while the steel has bilinear hardening.
Learning objectives:
1. Define a strain-softening geo-material that has different compressive and tensile behavior.
2. Embed reinforcing elements within a concrete solid.
3. Describe the stresses and strains in the concrete and steel composite structure.
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https://www.youtube.com/watch?v=rqHWA9IJn0g
This video illustrates the process for conducting the Direct Analysis Method for steel structures per the 15th Edition of the AISC Steel Construction Manual (AISC 360-16, Specifications for Structural Steel Buildings, Chapter C). This video performs design according to LRFD, though the ASD procedure is similar.
The primary benefit of performing structural analysis per the Direct Analysis Procedure is that the effective length factors K for all columns can be assumed equal to 1. Thus, the effective column length is equal to the unbraced length.
The necessary features for the Direct Analysis Method are:
1) Stiffness Reductions: apply 80% stiffness to all stiffnesses that contribute to the stability of the structure, plus an additional reduction to flexural stiffness of members with high compressive loads.
2) Second-Order Analysis: consider both P-Delta (capital Delta, accounting for deflections at column ends) and P-delta (lowercase delta, accounting for deflections along the lengths of columns) effects.
3) Notional Loads: lateral loads that account for structural imperfections, equal to 0.002 times the factored gravity loads on each story.
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https://www.youtube.com/watch?v=D5P2eAXx0Lg
In this tutorial, we learn how to use ETABS, a structural analysis and building design software package. ETABS has a lot to offer, so this video focuses on learning the basics of how to define a model, apply loads and load combinations, and interpret the analysis results.
We first define material and section properties. Then we draw the two-dimensional truss model. Finally, we place point and distributed loads and analyze the deflections, reactions, and axial force and moment diagrams.
Chapters:
0:00 Introduction
0:46 Welcome to ETABS
2:00 Navigating Views
3:33 Materials and Sections
5:30 Drawing the Structure
8:33 Modifying the Frames
11:06 Boundaries and Restraints
12:17 Load Patterns and Combinations
15:25 Applying Loads
19:33 Analysis and Results
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https://www.youtube.com/watch?v=X496Fm1peNU
In this video tutorial, we learn how to calculate the deflection of a truss using the Principle of Virtual Work. Also known as the Unit Load Method, this basis of this method is two analyze two structures:
(1) Real System - The structure with the design loads applied.
(2) Virtual System - The structure with a single load of magnitude one applied at the location where deflection is being calculated.
We combine the results of these two analyses by balancing out the external and internal work (i.e., strain energy) to compute the deflection of the truss at the location of interest.
For more information on conducting truss analysis, see:
Truss Analysis - https://youtu.be/Aoj-Hgx45Bo
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https://www.youtube.com/watch?v=GbC9bZ9en4Y