The Real Failure Mode

A young researcher studying Buckling Restrained Braces (BRB) once commented that a change made in their design had improved the failure mode such that fatigue of the yielding core no longer controlled the BRB’s performance. Upon investigation, the change had simply created a failure mechanism that developed BEFORE the steel would have fatigued had the change not been made. The fatigue life of the BRB had not changed – the rest of the system simply no longer had the capacity to survive until fatigue limits would have been reached. Thus, what was thought to be a benefit, was not. But the point is an important one.

…

Unreinforced CMU Wall with Diagonal Step Crack

Modern CMU construction almost always requires the installation of vertical reinforcement in the grouted cells of the CMU. However, addressing structural issues associated with unreinforced CMU construction prevalent prior to the 1990s can be daunting. In the author’s experience, today’s engineers do not know how to deal with, or adequately investigate, diagonal cracks in unreinforced CMU walls. …

Anchoring-to-concrete provisions in the American Concrete Institute’s Building Code Requirements for Structural Concrete (ACI 318) are used to calculate anchor design strengths that consider possible anchor failure modes. These design strengths are checked against calculated factored loads acting on anchors. ACI 318 anchoring-to-concrete parameters for calculating anchor design strengths are derived from testing and analysis that includes the use of a rigid fixture to apply tension load to anchors. Therefore, ACI 318 provisions for anchor design can be considered relevant if the fixture being attached can be considered “rigid.” …

Understanding and Minimizing Footfall Vibrations

Humans are restless creatures, always moving. They also tend to congregate and enjoy being restless together. Locate all this restlessness in just the wrong spot in a susceptible structure, and the structure is likely to join in – by vibrating in resonance. Structural amplification of human footfalls – walking, jogging, running, jumping, dancing – can be annoying at best and dangerous at worst. …

Most building codes worldwide have been developed to protect building occupant health and safety under likely loading, including earthquakes. Severe wind, snow, and live loads frequently occur during a building’s life. Therefore, in addition to protecting life safety, code requirements for these loads also result in a very low probability that buildings will be damaged by these loads. Earthquakes, however, occur rarely and most buildings never experience a significant earthquake. …

Part 2: How to Select a Reinforced Concrete Floor System

Reinforced concrete floor systems provide adequate resistance to vibration caused by a variety of sources because of their inherent mass and stiffness. General information on sources of vibration and acceptance criteria for typical office and residential occupancies was covered in Part 1 (STRUCTURE, September 2017). Vibration characteristics of reinforced concrete flat plate and wide-module joist systems were also discussed in Part 1, with useful guidelines to quickly ascertain when these reinforced concrete systems are adequate for various types of vibration excitations. …

Part 1: How to Select a Reinforced Concrete Floor System

Vibration analysis has become more commonplace in everyday practice. In office environments, the need for longer spans continues to increase. Open spaces, with minimal or no partitions and no filing cabinets, are becoming even more prevalent (typical electronic office), which translates to less damping to counteract vibrational effects.  …

Part 2: Right Way, Wrong Way with Software

Last month’s article (Structural Analysis, STRUCTURE, July 2017) was devoted entirely to model generation, the critical first step in an accurate analysis and design using the Finite Element Method (FEM). Remember, FEM is broken up into three basic steps: …

Part 1: Right Way, Wrong Way with Software

The increasing ease of performing a Lateral Analysis of a structure is becoming a double-edged sword: there are many benefits, but it can also be quite dangerous. A fair share of presentations and articles from seasoned engineers warn about colleagues losing a sense of the real behavior of structures, or that engineers today simply do not know how to design structures without a computer. …