There are too many reinforced concrete (RC) columns built before mid-1970s without sufficient transverse reinforcement. By now, we understand quite well the importance of transverse reinforcement in allowing a column to maintain its integrity under large displacement reversals in the nonlinear range of response. Poorly confined RC columns undergo a fast decay in resistance due to formation of criss-crossing inclined cracks, which can cause an abrupt failure or more gradual disintegration and trigger collapse of the structure. Those columns need to be strengthened to increase their drift capacity. Although there are several alternatives to retrofit RC columns, they often require specialized workmanship and equipment, and involved installation procedures. An easy-to-design and easy to implement retrofit technique is examined here. It consists of external post-tensioned clamps fastened around the column. Results of tests on full-scale RC columns furnished with the proposed clamps suggest the clamps can be effective in increasing column shear strength and drift capacity.

Experimental tests have been performed on interior post-tensioned (PT) slab-column (SC) connections over the past several decades. This paper presents a comprehensive database of 92 such tests performed on interior PT SC connections without shear reinforcement under direct shear. The data was then analyzed to compare the accuracy of the punching shear provisions of ACI 318-19, Eurocode 2 (2004), and CSA A23-19. Several key parameters were evaluated for the PT SC specimens including the concrete compressive strength, specimen geometry, bonded flexural reinforcement ratio, and minimum area of bonded flexural reinforcement; and their influence on the two-way shear strength of these connections was studied. Recommendations are made for possible modifications to the provisions of ACI 318-19 including the limit on the value of the concrete compressive strength f_c^'. Areas for further study, including size effect and bonded flexural reinforcement requirements, are highlighted.

This paper presents the results of an extensive test program that was aimed at investigating the flexural behavior of rectangular concrete-filled glass fiber-reinforced-polymer (GFRP) tube (CFFT) beams post-tensioned (PT) with unbonded steel tendons. The tests intend to simulate a number of design parameters, which are mainly governed by flexural loading. All beams were tested under four-point bending over a simply supported span of 3,000 mm [1229 in.]. Four full-size beams with an identical rectangular cross-sectional of 305 mm × 406 mm [12.0 in. × 16.0 in.] were constructed. The investigated test parameters were the number of tendons (2 or 3) and concrete strength (40 or 65 MPa) [5.80 or 9.43 ksi]. Besides, a proposed design equation as an extension to AASHTO (2012) equation based on a regression analysis of the test results herein to predicate the flexural capacity is established. The test results show that the cracking loads and post-cracking stiffness can be improved by increasing the number of strands. However, increasing the number of strands shows a slight effect on the ultimate capacity. The flexural capacities of PT CFFTs can be enhanced by increasing the concrete compressive strength without affecting their overall ductility. The proposed model successfully predicts the ultimate moment capacity of the tested beams and other results from the literature with an average of 1.08±0.16 and a COV of 14.5%. However, due to the limited test results in the present study and, in the literature, additional tests on the flexural behavior of PT rectangular CFFT beams are needed to further validate the accuracy of the model.

Fiber-reinforced polymer (FRP) reinforcements for concrete structures and civil engineering applications have become one of the innovative and fast-growing technologies to stop the rapid degradation of conventional steel-reinforced concrete infrastructure. FRP reinforcements for construction can be divided into three main types: 1. External sheets or plates to rehabilitate and repair existing concrete and masonry structures, and in some cases steel and wood structures; 2. Internal FRP bars or tendons for new and existing reinforced concrete structures, and 3. FRP stay-in-place forms to be filled with unreinforced or reinforced concrete. A considerable and valuable development and application’s work has been accomplished during the last three decades, leading to the development of numerous design guidelines and codes around the world, making the FRP-reinforcement technology one of the fast-growing markets in the construction industry. During the ACI Concrete Convention, Fall 2021, four full sessions were sponsored and organized by ACI Committee 440. Session S1 was focused on the bond and durability of internal FRP bars; Session S2 on codes, design examples, and applications of FRP internal reinforcements; Session S3 on external FRP reinforcements; and Session S4 on new systems and applications of FRP reinforcements, such as CFFT post-tensioned beams, GFRP-reinforced concrete sandwich panels, FRP-reinforced masonry walls, CFFT under impact lateral loading, near-surface mounted FRP-bars, and GFRP-reinforced-UHPC bridge deck joints.

The design of a cast-in-place, post-tensioned concrete, multi-cell box girder bridge under combined torsion, shear, and flexure is presented in this example. The bridge covers three spans of different lengths, supported by two abutments and two bents; its cross-section consists of three 12 ft (3.7 m) lanes, two 10 ft (3.0 m) shoulders, and two concrete barriers. The detailed procedure for the design based on ACI 318-14 is presented, and a comparison is done with the design results for: AASHTO LRFD 2017, EN 1992-1-1:2004, and MC-2010. With this example, the authors illustrate the differences between provisions of the aforementioned codes for design of torsional effects, outlining the different theories and approaches used for each of these.