Often Overlooked and Misunderstood

For over 40 years, the traditional pour strip in concrete construction has been an issue of contention between the engineer of record (EOR) and the contractor, and this challenge continues today. The EOR desires a high-quality slab, which requires more pour strips that are left open longer. The contractor wants faster construction, which requires fewer pour strips and pouring them back sooner. Shrinkage and restraint-to-shortening (RTS) are at the core of this age-old dilemma, and EORs should not have to sacrifice quality for cost and schedule.

Advancing First-Generation PBSD for Steel Buildings

Part 2: Case Studies

Implementing performance-based seismic design (PBSD) procedures for assessing existing buildings has generated interest in using similar approaches to design new buildings. The advantage of using these procedures is that designers can go outside the more prescriptive requirements of traditional design and have a more direct connection between expected performance and the design process (i.e., performance targets are explicitly defined upfront). This results in the engineer easily communicating the anticipated performance to the client and targeting a design that achieves beyond-code performance if desired. However, as PBSD was gaining popularity in practice approximately a decade ago, there had been limited published information into the relationship between standards for seismic design of new buildings and the seismic assessment of existing buildings.

Advancing First-Generation Performance-Based Seismic Design for Steel Buildings

Part 1: Background and Motivation

First-generation performance-based seismic design (PBSD) principles are outlined in the latest edition of the American Society of Civil Engineers and the Structural Engineering Institute’s ASCE/SEI 41-17: Seismic Evaluation and Retrofit of Existing Buildings referred to herein as ASCE 41. These PBSD principles have evolved since being introduced in the Federal Emergency Management Agency’s FEMA 273: National Earthquake Hazards Reduction Program (NEHRP) Guidelines for the Seismic Rehabilitation of Buildings (FEMA 1997). ASCE 41 provides analytical procedures and performance criteria to evaluate an existing building for a defined performance objective and to design seismic retrofit strategies if the criteria are not satisfied. This ability to explicitly define a performance objective and then assess a building against that objective has led practitioners to adopt ASCE 41 for use in new building designs to meet the intent of ASCE 7: Minimum Design Loads for Buildings and Other Structures, of which the latest edition is ASCE/SEI 7-16.

A Review of Design Considerations

Grout pockets are man-made holes in concrete structures (pre-installed before concrete placement or drilled after concrete placement) to allow the installation of anchors. The main benefit of using grout pockets is to allow equipment or structures to be installed after the concrete placement, providing more construction/installation schedule flexibility. In many non-modular projects, the equipment/machinery packages are typically completed and arrive at the construction site after most of the civil works at the site (including foundations) are completed. The grout pockets also provide extra installation tolerances and eliminate the risk of cast-in-place anchor movement during a foundation placement.

All wood is subject to some degree of seasoning, i.e., drying until it acclimates to the humidity conditions of the surrounding atmosphere at in-service conditions. Seasoning occurs when the wood is air-dried, dried in a kiln under controlled conditions, or subject to radio frequency drying. As wood loses (or gains) moisture, it will shrink (or swell) until it reaches equilibrium with the constantly changing level of moisture of its immediate environment. As shown in Figure 1, seasoning checks are separations of the wood fibers that develop along the length of lumber or timber due to shrinkage of the wood as it dries.

Gentle slopes are usually stable. As the slope’s inclination angle increases, the risk of failure increases accordingly. This can be attributed to the instability of the soil mass when the geometry results in the soil strength being unable to provide adequate support and its natural tendency to achieve stability and equilibrium. Failures in slopes usually occur in the form of soil movement, where the unstable mass topples or slides downwards or sideways to achieve stability.

Brick Masonry Façades and the Structural Engineer

Structural engineers typically have had little involvement with the design of brick masonry veneers other than the selection of lintels, shelf angles, and the attachment of these supports to the structure where warranted. In most cases, this is because brick masonry veneers are generally detailed prescriptively, which does not require engineering design. However, modern designs demanding high-performance enclosures and unique façade profiles increasingly require a structural engineer’s involvement for the design to conform to code requirements while achieving the intended effect.

Three-dimensional (3-D) volumetric construction is also known as concrete modular construction or Prefabricated Prefinished Volumetric Construction (PPVC). This construction method involves the stacking of rectangular factory-finished modular components on-site to form a complete building, similar to Lego® bricks. Joints are typically grouted with special interfacing details. To achieve speed and high productivity, the components have to be substantially completed with minimal site work. This article looks at some of the key design considerations and strategies that designers need to think about when using this type of construction method.

Understand the Consequences of Specifying Them to Resist Horizontal and Vertical Loading

Most structural engineers would not dream of deliberately violating any building-code provisions, but some are doing it on a regular basis – unwittingly. The problem area is concrete slabs cast on the ground. These concrete elements are frequently designed to serve as vertical supports for posts and columns, lateral ties, lateral-load transfer devices, and lateral bracing for walls. There is nothing wrong with relying on concrete slabs for these needs – as long as they are designed as structural slabs, like those in elevated floors, rather than common slabs on ground (SOG) that are relatively thin, reinforced with welded-wire fabric (WWF), if that, and contain control and isolation joints. It is this type of slab that is problematic for structural uses. …

Preventing Heat Loss Through Concrete Parapets

Conventional concrete parapets can form a thermal bridge that dissipates heat energy outside like large cooling fins, aided by cold winds whipping over the rooftop. One solution is to cast a structural thermal break between the parapet and the heated interior structure supporting it. …