thesis or dissertation chair
- Sayyafi, Ehssan Amir
Roofs are the most vulnerable part of the building envelope that often get damaged when subjected to hurricane winds. Damage to the roofs has a devastating impact on the entire structure, including interior losses and service interruptions. This study aimed at the development of a novel light-weight composite flat roof system for industrial, commercial and multi-story residential buildings to withstand Category 5 hurricane wind effects based on the Florida Building Code requirements for hurricane-prone regions, the strictest wind design code in the United States.
The proposed roof system is designed as a combination of two advanced materials: ultra-high performance concrete (UHPC), reinforced with high strength steel (HSS). The novel combination of these two materials in a specially designed cross section led to a lightweight low-profile ultra-thin-walled composite roof deck, with only 17 pounds per square foot self-weight, 4-inch overall depth and only ¾-inch thick flanges and webs, with no shear reinforcement or stirrup. Two groups of specimens, single-cell and multi-cell, were fabricated and tested in four-point flexure to determine the ultimate bending capacity and ductility of the system. Each group of specimens included two short-span (9 ft.) samples (due to the laboratory constraints) -- one specimen subjected to positive bending and the other one subjected to negative bending, representing the critical loading conditions including the effects of wind pressures. All specimens exhibited pure flexural failure in a ductile behavior and with no sign of shear failure. Finite element models of laboratory specimens were also developed and calibrated based on experimental data in order to project the performance of the system for larger and more realistic spans. The experimental work and the finite element analyses showed that the proposed roof system with its given section has adequate flexural and shear strength, and also meets serviceability requirements for a 20-foot long span. Moreover, connections for the roof system were proposed, including panel-to-panel connections and roof-to-wall connections.
In addition to safety, the other advantages of the proposed roof system in comparison to the equivalent reinforced concrete roofs include a three-fold reduction in self-weight, a three-fold reduction in overall profile height, and a five-fold reduction of steel reinforcement. Together, these advantages may lead to an increased span length beyond what is typically feasible for the conventional reinforced concrete slabs. All these features translate the proposed deck to a sustainable roof system.
- March 30, 2017
- High Strength Steel (HSS)
- Ultra-High Performance Concrete (UHPC)
- Ultra-High Performance Fiber Reinforced Concrete (UHPFRC)