Owen Rosenboom

Behavior of RC Beams Shear Strengthened with Bonded or Unbonded FRP Wraps

Reinforced concrete (RC) beams shear-strengthened with fiber-reinforced polymer (FRP) fully wrapped around the member usually fail due to rupture of FRP, commonly preceded by gradual debonding of the FRP from the beam sides. To gain a better understanding of the shear resistance mechanism of such beams, particularly the interaction between the FRP, concrete, and internal steel stirrups, nine beams were tested in the present study: three as control specimens, three with bonded FRP full wraps, and three with FRP full wraps left unbonded to the beam sides. The use of unbonded wraps was aimed at a reliable estimation of the FRP contribution to shear resistance of the beam and how bonding affects this contribution. The test results show that the unbonded FRP wraps have a slightly higher shear strength contribution than the bonded FRP wraps, and that for both types of FRP wraps, the strain distributions along the critical shear crack are close to parabolic at the ultimate state. FRP rupture of the strengthened ...

Fatigue Behavior of Prestressed Concrete Bridge Girders Strengthened with Various CFRP Systems

Synopsis: Carbon Fiber Reinforced Polymer (CFRP) materials provide a solution for the classical challenge facing bridge maintenance engineers: the upgrading of bridges whose service life has been exceeded but due to evolving demands must stay in service. Of particular concern are rural short span prestressed concrete bridges that may be required to carry loads above the initial design value. The CFRP strengthening systems presented in this paper have the potential to increase the ultimate capacity of such bridge girders. This research project is aimed at investigating the fatigue performance of CFRP strengthening systems for prestressed concrete bridge girders. Five 9.14 meter prestressed concrete bridge girders were tested under fatigue loading conditions: one as a control specimen and four strengthened with various CFRP systems including near surface mounted (NSM) bars and strips, and externally bonded sheets and strips. Results show that CFRP strengthened prestressed concrete bridge girders can withstand over two million cycles of fatigue loading equivalent to a 20 percent increase in live load with little degradation.

Reversed in-plane cyclic behavior of post-tensioned clay brick masonry walls for high performance modular housing

Publisher Summary The Partnership for Advancing Technology in Housing (PATH) program represents a partnership between industry, government, and researchers aimed to reduce risk of life, injury, and property destruction from natural hazards by at least 10% and reduce residential construction work illness and injuries by at least 20%, and improve durability and reduce maintenance costs by 50%. This chapter investigates the behavior of pre-stressed clay masonry walls that will then lead into a new modular housing technique, which will advance the goals of the PATH program. The pre-stress force for the walls was determined using a displacement-based design approach. It was stipulated that the prestress force in the walls should provide sufficient moment capacity to limit the wall drift ratio to 2% under the design level earthquake. It was determined that walls with unbonded tendons performed best in terms of strength, deformation capacity, and strength degradation. Application of galvanized steel confinement plates results in a marked effect on wall deformation capacity due to the ability of the plates to confine the compression toe region and stabilize the diagonal compression strut required for the wall rocking mechanism to develop.