Although the torsion design procedures in ACI 318-19 are simple and broadly applicable, the resulting designs tend to be conservative. To address this, clause 9.5.4.6 in ACI 318-19 permits the use of an alternative design procedure when designing members with an aspect ratio ≥ 3 for torsion, provided that the alternative procedure has been shown to agree with the results of comprehensive tests. This paper evaluates and compares the torsion design procedures in CSA A23.3:19 and the PCI Design Handbook 8th edition with those in ACI 318-19. Each of the three methods are found to show good agreement with 282 tests found in the literature. A comparison of the three concludes that the designs obtained using the ACI method generally require the most reinforcement. More economical designs for members subjected to relatively low and high torques can be obtained by using the PCI and CSA methods respectively. A design example of a spandrel beam using the three methods is presented, and then further conclusions are stated to guide practicing engineers on the relative strengths and weaknesses of each procedure.

This paper describes the collapse of the Concorde Overpass that was partly due to improper hanger reinforcement details in the disturbed region (D-region) of the beam seat. A review of the evolution of the hanger reinforcement details in dapped end beams given in different versions of the PCI Design Handbook is presented. The results of a series of experiments on dapped end beams with different hanger reinforcement details are described. Guidance from these tests and other experiments on the details of anchorage of the hanger reinforcement in dapped end beams is provided.

This paper presents a description and comparison of several experimentaltechniques used to determine the effective prestressing force in pretensionedprestressed concrete girders. The effective prestressing force was determined by threemethods: (1) using vibrating wire strain gages that were embedded in the girders duringfabrication; (2) load testing the girders to determine flexural cracking and crack re-opening loads and then back calculating the losses; and (3) exposing a length ofstrand, attaching resistance strain gauges on the strands, and flame-cutting theinstrumented strands.Several instruments were used to determine the flexural crack initiation and crack re-opening loads. These included crack detection gages, concrete surface strain gauges,and LVDTs, as well as visual observations. Use of data from the strain gauges placed atthe bottom surface of the girders was determined to be the most effective way ofdetecting flexural crack initiation and re-opening. Cracking loads determined fromvisual observation were significantly larger than those determined from the straingauge data.The back-calculated prestress losses determined from the measured flexural crackinitiation and re-opening loads of the girders were significantly larger than thosedetermined from other experimental methods and those predicted by the PCICommittee and AASHTO LRFD methods. Losses determined by the other experimentalmethods and the predictions correlated more closely with those back-calculated usingvisually-observed cracking loads.These results indicate that prediction of losses based on the measured flexuralcracking and crack re-opening loads using the basic theory of mechanics results in anoverestimation of prestress losses. Consequently, girders may undergo flexuralcracking and crack re-opening at lower loads than predicted using the basic theory ofmechanics.

Mechanical characteristics of High Performance Fibre Reinforced Concrete subjected to elevated temperatures up to 700 C were experimentally investigated in this paper. Three different concretes were prcpared a normal strength concrete (NSC with nominal 28 days strength of 40 MPa) and two High Performance Concretes (HPCI with 28 days strength of 82 MPa and HPC2 with 28 days strength of 94 MPa). Fibre reinforced concretes were produced by addition of steel or polypropylene fibres in the above mixtures at dosages of 40 Kg/m3 and 10 Kg/m3 respectively. A total of 9 concrete mix- tures were produced and fibres were added in six of them. At the age of 4 months specimens were heated to maximum temperatures of 100, 300, 5OO and 700 C. Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. Reference tests were also performed at air temperature (20 C). Residual strength of NSC and HPC1 was reduced almost linearly up to 700 C and 500 C respectively but the latter had an explosive spalling at 700 C. Residual strength of HPC2 was sharply reduced up to 300 C and explosive spalling occurred at higher temperatures. Addition of steel fibres increased the percentage of residual strength up to 300 C hut spalling still occurred in HPC1 and HPC2 at 700 C and 500 C respectively. Such an explosive behavior was not observed when polypropylene fibres were added in the mixtures.

Based on four strength parameters testing of three high-performance concrete (HPC) design mixes and parametric studies, the following conclusions have been made. Creep and shrinkage strains of HPC are lower than those in conventional concrete. Amount and type of coarse aggregates affect the value of modulus of elasticity. The modulus of elasticity of HPC should be determined through experiments with local materials. Beam sections that have large bottom flange are efficient for HPC application. The most significant property of HPC prestressed beam is compressive strength at release. Allowable compression at release has the most impact on span capacity, while allowable tension at service has minor impact. Prestress loss can be reasonably predicted by either the proposed method or AASHTO LRFD Lump Sum method. PCI deflection multipliers at final time are not accurate. The proposed multipliers which are the functions of creep coefficient can be used for conventional and HPC members.