Concrete Slab Strips Research Articles

Scaling Mode Shapes in Output-Only Systems by a Consecutive Mass Change Method

In operational modal analysis (OMA) mode shapes can be obtained only with arbitrary normalization. There are many applications where mass normalized mode shapes are required, such as response prediction and stress analysis. A method to scale the mode shapes in OMA is to modify the dynamic behaviour of the structure by adding masses and then to use the modal parameters of both the original and modified structure. Several mass change methods have been proposed in recent years for estimating the scaling factors, where a distributed array of added masses are needed to obtain good results. In this work a new mass change approach based on performing several individual mass changes is presented. This approach requires only a small number of masses that are located at different points in each individual experiment. The results of the individual tests are then combined to estimate the scaling factors. The approach is developed and validated by measurements carried out on a 15-tonne prestressed concrete slab strip and a steel cantilever beam. The results show that a good accuracy can be obtained by this method when a proper mass change strategy is used.

Robust saturated control of human-induced floor vibrations via a proof-massactuator

This paper is concerned with the design of a robust active vibration control system thatmakes use of a proof-mass actuator for the mitigation of human-induced vibrations in floorstructures. Ideally, velocity feedback control (VFC) is unconditionally stable and robust tospillover effects, interlacing of poles and zeros of collocated control is then accomplished.However, the use of a proof-mass actuator influences the system dynamics and thealternating pole-zero pattern of the system formed by the actuator and structure is nolonger fulfilled. However, a controlled migration of the two zeros of the root locus plot atthe origin, resulting from the acceleration output, can be achieved by adding afeed-through term (FTT) to the structure acceleration output. That is, the FTT enables usto control the position of a pair of complex conjugate zeros (an anti-resonance in thefrequency domain). This paper proposes the introduction of an FTT designed in such away that the anti-resonance at the origin is located between the actuator resonanceand the structure fundamental resonance. Hence, an integral controller leads toinfinite gain margin and significant phase margin. Simulation and experimentalresults on a concrete slab strip have validated the proposed control strategy.Significant improvements in the stability properties compared with VFC are reported.

Whole-building behaviour of bonded post-tensioned concrete floor plates exposed to fire

Abstract This paper discusses the whole-building behaviour of post-tensioned concrete floor plates under fire conditions. Based on the results of eight fire tests on one-way spanning bonded post-tensioned concrete slab strips, recently conducted by the authors, a nonlinear finite element model was developed to model an entire typical concrete floor plate. The considered floor plate was post-tensioned using bonded tendons and was supported on traditional reinforced concrete columns. The overall objective of the study was to provide an understanding of the structural response and modes of failure of these floor plates under fire conditions. The mechanical and thermal material nonlinearities of the floor’s components, consisting of the concrete, grout, prestressing tendon, and the anchorages, as well as the reinforced concrete columns, have been considered in the model. The interface between the tendon and grout was also considered, allowing the bond behaviour to be modelled and the tendon to retain its profile shape during the deformation of the floor. The model has been validated against published finite element results on a floor plate under normal temperature conditions. The temperature distribution throughout the floor slab and supporting columns, together with the developed displacement and stress due to heating, and the overall fire resistance of the floor were predicted by the model. Furthermore, the variables that influence the structural behaviour comprising different natural fires, applied static load during fire, use of non-tensioned reinforcement, as well the difference between unbraced and braced frames were investigated in a parametric study. The study has shown that the failure mode of the floor under fire conditions is mainly due to tensile splitting along the tendons that extended to the top surface, while at ambient conditions the mode of failure is punching shear. The restraint provided by shear walls in the considered braced frame and the use of non-tensioned flexural reinforcement affected the vertical displacement behaviour under fire conditions, but did not affect the fire resistance due to the predicted tensile splitting failure mode. From the studies presented it is concluded that the design fire resistance of the floor specified in Eurocode BSEN1992-1-2 is acceptable, while that in the UK code BS8110 is unconservative and should be modified.

Load–deflection behaviour of restrained RC slab strips

This paper presents results of an experimental investigation into the load–deflection behaviour of restrained reinforced concrete slab strips subjected to uniformly distributed loads beyond the yield load. A method incorporating compressive membrane action is proposed to predict the behaviour. Results indicate that the proposed method can predict the actual trends for certain scenarios. Previously reported methods have been studied and the results compared with those from the current work.

Arching action in high-strength concrete slabs

The corrosion of reinforcement in bridge deck slabs has been the cause of major deterioration and high costs in repair and maintenance. This problem could be overcome by reducing the amount of reinforcement and/or altering the location. This is possible because, in addition to the strength provided by the reinforcement, bridge deck slabs have an inherent strength due to the in-plane arching forces set up as a result of restraint provided by the slab boundary conditions. This is known as arching action or Compressive Membrane Action (CMA). It has been recognised for some time that laterally restrained slabs exhibit strengths far in excess of those predicted by most design codes but the phenomenon has not been recognised by the majority of bridge design engineers. This paper presents the results of laboratory tests on fifteen reinforced concrete slab strips typical of a bridge deck slab and compares them to predicted strengths using the current codes and CMA theory. The tests showed that the strength of laterally restrained slabs is sensitive to both the degree of external lateral restraint and the concrete compressive strength. The tests particularly highlighted the benefits in strength obtained from very high strength concrete slabs. The theory extends the existing knowledge of CMA in slabs with concrete compressive strengths up to 100 N/mm2 and promotes more economical and durable bridge deck construction by utilising the benefits of high strength concrete.

Arching action in high-strength concrete slabs

The corrosion of reinforcement in bridge deck slabs has been the cause of major deterioration and high costs in repair and maintenance. This problem could be overcome by reducing the amount of reinforcement and/or altering the location. This is possible because, in addition to the strength provided by the reinforcement, bridge deck slabs have an inherent strength due to the in-plane arching forces set up as a result of restraint provided by the slab boundary conditions. This is known as arching action or Compressive Membrane Action (CMA). It has been recognised for some time that laterally restrained slabs exhibit strengths far in excess of those predicted by most design codes but the phenomenon has not been recognised by the majority of bridge design engineers. This paper presents the results of laboratory tests on fifteen reinforced concrete slab strips typical of a bridge deck slab and compares them to predicted strengths using the current codes and CMA theory. The tests showed that the strength of laterally restrained slabs is sensitive to both the degree of external lateral restraint and the concrete compressive strength. The tests particularly highlighted the benefits in strength obtained from very high strength concrete slabs. The theory extends the existing knowledge of CMA in slabs with concrete compressive strengths up to 100 N/mm2 and promotes more economical and durable bridge deck construction by utilising the benefits of high strength concrete.

両端固定一方向性中空スラブに関する実験的研究 : 中空スラブの孔と直交方向のせん断破壊について(その2)

This paper discusses the experimental results of reinforced concrete slab strips whose circular hollows are arranged perpendicularly to the logitudinal direction. In this paper, a series of slab strips were tested under the conditions of no shear reinforcement and short term loading in a very stiff surrounding frame. The experimetal results showed that the hollow slab strips of this type tends to produce shear failure and the failure phenomena are very complicated due to stress concentration effect. The author analyized these shear failure phenomena and showed that the failure modes can be explained by simple calculations.