ACI 364.2T-08 INCREASING SHEAR CAPACITY WITHIN EXISTING REINFORCED CONCRETE STRUCTURES

ACI 364.2T-08 INCREASING SHEAR CAPACITY WITHIN EXISTING REINFORCED CONCRETE STRUCTURES.
Shear reversals are common on continuous structures with variable loading patterns. Shear strengthening schemes generally require that the additional shear reinforcement remain functional throughout the anticipated failure mecha- nism, which is usually fexural in nature. For bonded reinforcements, this typically requires some form of anchorage to ensure attachment across the shear cracks after the initiation of debonding. The debonding mechanism is governed by the tensile strength of concrete, and is diffcult to prevent. Although the use of anchorage for bonded shear reinforce- ment provides attachment after debonding, a close examination of strain compatibility with the existing internal shear reinforcement is required to ensure that all shear reinforcing elements will reach or exceed the intended local design limit when the member reaches the structural capacity. Schuman (2004) provided one such anchorage approach for the use of externally bonded FRP shear reinforcement. An important part of any shear strengthening design is the anticipated sequence of strain generation and attainment of the intended design limits between the conventional internal steel reinforcement and the additional shear reinforcement. The modulus alone will not always dictate which elements are the most highly strained across a given shear crack.
References ACI Committee 437, 2003, “Strength Evaluation of Existing Concrete Buildings (ACI 437R-03),” American Concrete Institute, Farmington Hills, MI, 28 pp. ACI Committee 440, 2002, “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (ACI 440.2R-02),” American Concrete Institute, Farmington Hills, MI, 45 pp. ACI Committee 440, 2006, “Guide for the Design and Construction of Concrete Reinforced with FRP Bars (440.1R-06),” American Concrete Institute, Farmington Hills, MI, 44 pp. ACI Committee 546, 2004, “Concrete Repair Guide (AC,” American Concrete Institute, Farmington Hills, MI, 53 pp. Carolin, A., and Täljsten, B., 2003, “Behavior of Concrete Structures Strengthened in Shear with CFRP,” Proceed- ings of the Sixth International Symposium on FRP Reinforcement for Concrete Structures (FRPRCS-6), Singapore, World Scientifc, pp. 467-476. Raina, V. K., 1994, Concrete Bridges; Inspection, Repair, Strengthening, Testing and Load Capacity Evaluation, McGraw-Hill, New York, 493 pp. Schuman, P., 2004, “Mechanical Anchorage for Shear Rehabilitation of Reinforced Concrete Structures with FRP: An Appropriate Design Approach,” PhD thesis, Department of Structural Engineering, University of Cali- fornia at San Diego, La Jolla, CA, 528 pp. Wong, R. S. Y., and Vecchio, F. J., 2003, “Towards Modeling of Reinforced Concrete Members with Externally Bonded Fiber-Reinforced Polymer Composites,” ACI Structural Journal, V. 100, No. 1, Jan.-Feb., pp. 47-55.ACI 364.2T pdf download.