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Fiber-reinforced polymer (FRP) strengthening offers many well-documented benefits for the retrofit of existing reinforced concrete (RC) structures. The main drawback in using FRP for such applications, however, is the reduction in ductility capacity after strengthening. This loss in ductility has led worldwide codes to not consider redistribution of bending moments in continuous FRP-strengthened RC beams. This implies that an unstrengthened continuous RC beam that was previously designed under assumptions of moment redistribution (MR) and is to be strengthened with FRP must now be redesigned according to full elastic distribution of bending moments. This could lead to onerous conditions in such strengthening applications. This paper sets out a rationale for the possible appropriate use of redistribution principles for FRP-strengthened beams. Analytical results show that if a section can develop a curvature ductility capacity greater than 2.0, it is likely that redistribution in the order of at least 7.5% can be achieved. These results are presented and further discussed in this paper. © 2008, American Concrete Institute.

Routine management and maintenance of civil infrastructure is undertaken based on structural health indicators from qualitative information gathered during inspections. The need to measure and collect data reflective of the true state of the infrastructure is crucial for proper management of the system. Presented in this paper are methods for incorporating field measurements for improved condition assessment. A full scale field deployment of a wireless, low-cost and automatic system for structural health management and condition assessment of highway structures is shown to demonstrate the ability of obtaining the necessary behavior characteristics. A short-span integral-abutment bridge was instrumented with a developed wireless sensor system measuring strain, in real time through a single network, monitoring the behavior of the structure under various loading conditions. Measurements validated the performance characteristics of the bridge, including transverse moment distribution, end fixity, and composite action of the girders and bridge deck.

Results of bending tests on three continuous reinforced concrete slab strips are compared with calculations according to linear, nonlinear, and limit analysis approaches, as well as with code provisions. It is demonstrated that the reduced ductility properties of cold-deformed and coiled small-diameter reinforcing bars and wires may result in dangerous strain localizations, impairing rotation capacity, permissible moment redistribution, and ultimate strength. A nonlinear analysis method for refined deformation investigations is presented, and minimum ductility requirements for reinforcing steel are suggested.

The effective width and equivalent frame analysis methods are applied to a flat plate test specimen. The theoretical moment distribution and lateral drift show poor agreement with the test specimen results. A modified two-beam analytical model is proposed. This model allows for more appropriate modeling of the slab cracking in negative and positive bending regions. The modified model is able to reproduce both the slab moment distribution and lateral drift observed in the test specimen. Effective width factors, a, and slab cracking factors, β, are suggested for use in modeling of flat plates for lateral and gravity load analysis.

ACI Building Code 318-89 and Canadian Standard CAN3-A23.3-M84 give a design method for slab-column connections transferring shearing forces and bending moments. The code commentaries apply the method and give equations for design of critical sections adjacent to interior columns. Difficulties arise when use of the same equations is extended to critical sections adjacent to corner and edge columns. A solution to this problem and revisions of the code commentaries are proposed. The proposal covers the design of critical sections farther away from the column face; this design is necessary when shear reinforcement is provided.

The Australian concrete codes, NAASRA and AS3600, permit moment redistribution in prestressed concrete structures for design at the strength ultimate limit state. Provided the sections considered have sufficient ductility, the redistributed moment at any intermediate support is taken as a percentage of the elastically determined and factored negatives moment, including the secondary prestress effects. The magnitudes of these allowable redistrubtions are directly related to the ductility of these sections. There is a logical relationship between the magnitude of these redistributions and the ultimate capacity and ductility of the relavant cross sections. Conversely, the rules in ACI 318-89 are shown to be illogical. The inclusion of prestress secondary moments with other load moments has been a subject of considerable controversy, and this paper illustrates, from a designer's point of view, that these secondary moments can be considered to be present at the strength ultimate limit state and that they are often beneficial.

This paper presents graphs for the immediate solution of the problem involving homogeneous structures with a variable structural system.

In 1977, the ACI Building Code introduced a torsional limit design method for the design of spandrel beams subjected to torsion. This very economical method utilized the redistribution of moments between the spandrel beam and the adjoining floor beams. This paper provides a theoretical method to predict the two disticnt redistributions of moments and to clearly describe the 3-stage behavior of the spandrel beam.

This paper addresses the problem of flexural ductility and redistribution on moments in staticaly indeterminate, partially prestressed linear members. The influence of prestresing on the ductility is discussed, and recommendations are made with respect to the treatment of the hyperstatic prestress moments at the ultimate limit state, vis-avis the allowable percentage of moment redistribution. Hyperstatic prestress forces result when the imposed deformations due to prestressing are restrained or prevented by the support conditions of the structure.

The nonlinear behavior of reinforced concrete frames with sidesway is governed by two effects: first, the nonlinearity of materials due to cracking and the plastic behavior of materials, and second, the nonlinearity of geometry caused by the second‐order deformation. These two effects may interact, and the whole phenomenon is known as the nonlinearity of geometry and materials. Reinforced concrete frames are frequently used to resist wind or earthquake forces. These forces will accentuate the complexity of the frame behavior because of the continuous change of the shape of the bending moment diagram. The change of moment diagram will in turn affect the magnitude of the cumulative plastic rotations. A trial and error method was devised to predict theoretically the moment‐load curves of reinforced concrete frames throughout the loading history. This method utilized the trilinear moment‐curvature curve for critical sections suggested by Macchi [8], as well as the principle of virtual work to express...

THE RESULTS OF A STUDY OF THE INFLUENCE OF THE STUFFINSS OF THE SUPPORTING BEAMS ON THE DISTRIBUTION OF MOMENTS WITHIN TYPICAL INTERIOR PANELS OF REINFORCED CONCRETE FLOOR SLABS ARE PRESENTED. THE RESULTS ARE PRESENTED IN TERMS OF A BEAM STIFFNESS PARAMETER AND THE PANEL SHAPE. IT IS SHOWN THAT ONCE THE BEAM STIFFNESS PARAMETER EXCEEDS 2, AS WILL BE THE CASE IN A LARGE PORTION OF THE SLABS SUPPORTED ON BEAMS ON ALL FOUR SIDED OF THE PANEL, THE MOMENT DISTRIBUTIONS ARE RELATIVELY INSENSITIVE TO FURTHER INCREASES IN BEAM STIFFNESS. /AUTHOR/

A load test on a portion of a six-story flat plate building was carried out to evaluate performance under high overload.