Structural Screws

Uncategorized
There are many different brands and products of structural screws designed for fastening wood members (SDS screws, LedgerLOK, HeadLOK, timberLOK). These structural screws are typically designed to replace lag screws without requiring pre-drilling, resulting in significant cost savings for labor. Most of these products have a similar diameter of slightly…

Attaching to Concrete Shear Walls

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When dragging a heavy collector load into the top of a concrete shear wall, concrete breakout in shear can be fairly easily prevented by adding anchor reinforcement. This leaves 2 failure modes to address: anchor bolt shear, and pryout. Anchor bolt shear is easy to increase by simply adding more…

Singly Reinforced Concrete Beam Strength Limits

Derivations, Structural Engineering
Moment Capacity Given: axial force, P (tension positive), which may include axial tension from torsion Assumptions: one layer of rebar near tension face is resisting all tension; ignore rebar layer near compression face Variables: applied axial force (tension positive) resultant force at concrete compression block (tension positive / compression negative)…

Deflections

Derivations, Structural Engineering
Codes limit deflections to a fraction of the span length, assuming fixed supports at each end of the span. But what happens if we use spring supports instead of fixed supports? Where should the deflection be measured from? This issue becomes even more pronounced with finite element analysis where the…

Wood Shear Wall Stiffness

Uncategorized
Reverse Engineering the NDS Deflection Formula The 3-term formula for shear wall deflection in the NDS standard is: (equation 4.3-1)     Where: There are several unit conversions baked into the formula, and the input shear is given in units of pounds per foot. To convert this to stiffness in…

Written Explanation of Irregular Wood Diaphragm Calculations

Structural Engineering
The attached document is an incomplete written guide to running irregularly shaped flexible diaphragm calculations by hand. Most of the information within this document is a substantially condensed version of “The Analysis of Irregular Shaped Structures Diaphragms and Shear Walls” by R. Terry Malone and Robert W. Rice. If you…

Timoshenko Beam Calculator and Plot

Calculation Templates, Structural Engineering
https://www.desmos.com/calculator/i8cxyq9ptf This Desmos calculator uses the equations laid out in the “Diaphragm Deflection” post following the “Timoshenko Beam Formulas” post derivation. These equations are a derivation of the governing equation for a Timoshenko beam but using a similar method to the NDS in order to find a useful solution with…

FEA Program Coordinate Systems

Derivations
Global Coordinate System Variables: x, y, z Local Coordinate System Variables: n (local x direction) s (local y direction) t (local z direction) Natural Coordinate System Used for isoparametric components (“xi”: natural x direction) (“eta”: natural y direction) (“zeta”: natural z direction)

Finite Element: Q8 Quadrilaterals

Derivations, Structural Engineering
The following are notes that may be helpful when implementing the stiffness matrix for a Q8 quadrilateral. These notes supplement the following YouTube lectures by Dr. Clayton Pettit: Finite Element Method: Quadrilateral Elements Finite Element Method: Isoparametric Elements Shape Functions Throughout this derivation, we will use the following shape functions:…

Cantilever Beam Formulas

Structural Engineering
Case 1: Uplift resisted by point load at end of backspan Point Load at Free End (at free end) Uniformly Distributed Load on Cantilever (at free end) Case 2: Uplift partially resisted by backspan dead load Backspan Reaction This case uses available dead load on the backspan to help clamp…