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Optimization of prefabricated joists
Abstract
This dissertation investigated the performance of precast prestressed concrete joists used for floor or roof members. The main objective of this study was to create a joist with web openings. The benefits of web openings are two-fold. First, a reduction of the double tee weight itself is achieved. Second, the web openings are used to run the mechanical ducts and electrical wires through the webs rather than beneath them, which reduces floor-to-floor height and results in an overall building height reduction. In the first part of the study, the prestressed precast double tees were investigated. Two groups of specimens were designed to investigate the number of openings, strand profile, and different reinforcement details around the openings. Since the web openings reduce the stiffness of the double tee, deflections, anchorage of the reinforcement, and vibrations were major issues. A design procedure and design aid in the form of tables were developed. The results indicate that the behavior of the double tee with web openings is the same as the behavior of the conventional double tee. In the second part of the study, the development of a new hybrid joist was investigated. In this system, the benefits of both open web steel joists and prestressed precast double tees were combined. The new hybrid joist system involves using prestressed precast trusses to support a cast-in-place deck. The system can be all precast where a flange deck is prefabricated in a second stage with the truss to make a T-shape whose web is a prestressed truss. The joist would accommodate different span lengths and spacings. This system is light, strong, and allows mechanical ducts to penetrate through its depth. Analytical investigation was conducted to evaluate the performance of the hybrid joist. Several series of specimens were designed to investigate the behavior of the joist. Since the joist is a new system, flexural behavior, deflections, anchorage of the reinforcement and vibrations were major issues. The behavior of the joist was promising for introducing a new concept of hybrid joist. A design procedure and design aid in the form of tables were developed to help designers in the preliminary selection of the joist sizes. The results indicate that the structural behavior of the hybrid joist is comparable to that of double tees.
Subject Area
Civil engineering
Recommended Citation
Saleh, Mohsen Ahmed, "Optimization of prefabricated joists" (1996). ETD collection for University of Nebraska-Lincoln. AAI9712524.
https://digitalcommons.unl.edu/dissertations/AAI9712524