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Analytical and experimental studies were undertaken to assess and improve modeling techniques for capturing the nonlinear behavior of flat-plate systems using results from shake table tests of two, approximately one-third scale, two-story reinforced concrete and posttensioned concrete slab--column frames. The modeling approach selected accounts for slab flexural yielding, slab flexural yielding due to unbalanced moment transfer, and loss of slab-to-column moment transfer capacity due to punching shear failure. For punching shear failure, a limit state model based on gravity shear ratio and lateral interstory drift was implemented into a computational platform (OpenSees). Comparisons of measured and predicted responses indicate that the proposed model was capable of reproducing the experimental results well for an isolated connection test, as well as the two shake table test specimens. DOI: 10.1061/(ASCE)0733-9445(2009)135:2(147) CE Database subject headings: Shake table tests; Concrete slabs; Connections; Punching; Limit states; Post tensioning; Plates.

The primary objective of in-situ load testing is to evaluate the safety and serviceability of an existing structural system with respect to a particular load condition and effect. In light of technological advances in construction methods, analytical tools and monitoring instrumentation, new different evaluation criteria are being proposed in addition to different in-situ load test methods. Some criteria may be more appropriate than others based on the expected damage and failure mechanisms of the structure being considered. The companion paper describes the rationale and application of both a consolidated and an alternative approach to the determination of load level, loading procedure and instrumentation requirements for two case studies. This paper discusses in detail the evaluation criteria and outcomes of these two field projects consisting of a posttensioned concrete slab with structural deficiencies due to tendon and mild reinforcement misplacement and a floor bay of a two-way reinforced concrete slab showing cracking at the positive and negative moment regions. After discussing the relative merits of the evaluation methodologies and the significance of their respective acceptance thresholds, concepts for the development of a new global criterion are discussed. DOI: 10.1061/(ASCE)0887-3828(2008)22:4(217) CE Database subject headings: Concrete structures; Field tests; Instrumentation; Load tests; In situ tests; Concrete slabs; Serviceability; Safety.

The primary objective of in-situ load testing is to assess the safety and serviceability of an existing structural system with respect to a particular load effect. At this time, the most appropriate loading level and procedure, as well as the associated evaluation criteria are being reconsidered in light of technological advances in construction methods, analytical tools, and monitoring instrumentation. The in-situ load test method for reinforced concrete systems described in the ACI Building Code Requirements for Structural Concrete, namely the 24-h load test method and its evaluation criteria, has been in use for several decades, but may no longer serve the needs of contemporary construction and engineering practices. As a result, other load test methodologies and associated evaluation criteria are under development. This paper and a companion paper describe the rationale and application of an alternative approach to the determination of load level, loading procedure, instrumentation requirements, evaluation criteria and outcomes for two field projects. The first case study is relative to a posttensioned concrete slab where many areas were characterized by tendon and reinforcement misplacement, resulting in inadequate flexural strength and inadequate shear/flexure transfer at column/slab intersections. The second case study is the structural evaluation of a typical floor bay of a two-way reinforced concrete slab system, presenting distributed cracking at the positive and negative moment regions. Finite-element-method models were created for both structures to aid the load test design. The numerical models validated the field observations. DOI: 10.1061/(ASCE)0887-3828(2008)22:4(207) CE Database subject headings: Concrete structures; Field tests; Instrumentation; Load tests; In situ tests; Concrete slabs.

The influence of concentrated reinforcement in the immediate column region, the use of high-strength concrete slabs, as well as using puddled fiber-reinforced high-strength concrete in the slab in a region close to the column were investigated. The slab concrete strengths of the specimens were 30, 35, 40, 55, 65, and 90 MPa. The performance of the slab-column specimens tested was investigated, including the punching shear capacity, cracking on the top of the slabs around the columns, and the stiffness of the slab-column connections. Predictions using different code equations are compared to the experimental results obtained from the slab-column connections tested in this study and those tested in other studies. The beneficial effects of using concentrated flexural reinforcement, high-strength concrete and puddled fiber-reinforced high-strength concrete are demonstrated. DOI: 10.1061/(ASCE)0733-9445(2008)134:3(448) CE Database subject headings: Concrete slabs; Steel fibers; Shear strength; Punching; Columns; Connections.

This paper presents the first series of validation tests for a patented shear reinforcement system for reinforced concrete flat slabs. The system, called 'Shearband,' consists of elongated thin steel strips punched with holes, which undulate into the slab from the top surface. The main advantages of the new reinforcement system are structural effectiveness, flexibility, simplicity, and speed of construction. Four reinforced concrete slabs were tested in a specially designed test rig. The slabs reinforced in shear exhibited ductile behavior after achieving their full flexural potential, thus proving the effectiveness of the new reinforcement. This paper reviews briefly existing types of shear reinforcement and identifies the need for more efficient and economic solutions. Details of the experimental setup and results are given, including strain and deflection measurements as well as photographs of sections through the slabs. Finally, comparisons are made with the ACI 318 and BS8110 code predictions, which confirm that the system enabled the slabs to avoid punching shear failure and achieve their flexural potential. In addition, both codes are shown to lead to conservative estimate of flexural and punching shear capacities of reinforced concrete slabs. DOl: 10.1061/(ASCE)0733-9445(2003)129:9(1164) CE Database subject headings: Concrete slabs; Concrete, reinforced; Validation; Shear resistance; Tests.

It is well known that cracking in concrete slabs significantly influences their service life. Concrete shrinkage may be the principle reason for the initial crack formation in the slabs. This paper presents an attempt to provide an analytical tool for the prediction of stress distribution in reinforced concrete slabs after undergoing matrix shrinking restrained by the reinforcing bars. The model incorporates the material parameters of the reinforcing bar and the concrete matrix, and it enables prediction of the stress development in concrete with time.

Ten large-scale tests on floors comprising hollow-core slabs supported on beams were carried out. All tests ended in web shear failure of slabs close to the supports of the beam. In one test the shear resistance was not reduced, but in others was only 40-77% of the reference value measured on nonflexible supports. In one test yielding of the reinforcement in the supporting beam preceded failure. In other tests the beams did not yield and their deflection at slab failure was very small, typically [L.sub.b]/1,000-[L.sub.b]/300. Reduction of shear resistance is due to transverse deformation of the slab ends resulting from deflection of the beam. The reduction is so great that it must be considered in design, even though collapses due to such reduction, thanks to the high safety factors applied, have neither occurred nor are likely to occur in conventionally designed floors.

Previous test results of two-way fully restrained reinforced concrete slabs are used to optimize the model parameter values involved in a finite element program. The parameters whose sensitivities control the simulation process are identified through extensive parametric studies using both the displacement and load control strategies, and values are identified for them. Use of such values has been shown to guarantee reliable predictions of both the peak load and the corresponding deflection of arbitrary fully restrained rectangular slabs. A series of numerical predictions of over 850 'computer model' slabs are undertaken, varying the geometric and material properties, as well as the reinforcement ratios. The result is used for developing charts that may be used for the strength and displacement determination of arbitrary fully restrained slabs. The charts are used for the predictions of 36 previously tested slabs, in which the slab strength is predicted to within a mean accuracy of 2%, and the deflection is predicted to within a mean accuracy of 4%. Other practical applications of reliable numerical predictions are discussed.

A numerical model has been developed to reproduce the punching failure in reinforced-concrete structures. It is characterized by an efficient triaxial strength criterion for concrete, a nonassociated flow rule reproducing the concrete dilatancy observed experimentally, and a cracking model accounting for the brittleness of concrete failure under various states of stress. The simulation of punching failure in a circular slab is successfully performed as the localized mode of failure - characterized by an inclined crack - is reproduced. It is shown that punching failure is initiated by the coalescence of microcracks inside the slab, followed by a crack propagation towards the corner of the slab-column intersection. A parametric analysis of the punching failure demonstrates that (1) punching failure is due to tensile failure of concrete along the inclined punching crack and is not due to compressive failure; (2) increasing the percentage of reinforcement reduces the state of internal cracking resulting in an increase of the failure load and a reduction of the ductility; and (3) the size effect observed experimentally is reproduced and a size-effect law is proposed.

A simple procedure for calculating deflections of reinforced concrete two-way slabs is presented in this paper. The material model for reinforced concrete based on the effective stiffness approach has been implemented in a finite-element program incorporating Mindlin-plate-bending elements. Uncracked concrete is treated as an isotropic linear elastic material, and after cracking, the concrete is considered to be an orthotropic material. The reduced stiffness coefficients after cracking are calculated from the effective moments of inertia in the x- and y-directions. These effective moments of inertia are determined using the formula proposed by Branson (1963). The influence of both bending and torsional moments is included in the formulation. The proposed model has been verified by comparisons with results from tests on slabs with various loading and boundary conditions. A study has also been undertaken to check the sensitivity of the proposed formulation when applied to the analysis of slabs with different reinforcement ratios, boundary conditions, and reinforcement orientations.

The effect of reinforcement corrosion on the flexural strength of a uniformly loaded and simply supported one-way slab was investigated. In addition to the flexural strength, the effect of different degrees of reinforcement corrosion on the deformational behavior, ductility, and the mode of failure of the slabs were also evaluated. The critical level of reinforcement corrosion that renders the strength contribution of steel negligible was evaluated by comparing the strengths of slabs with highly corroded reinforcement with the strengths of plain concrete slabs. In order to induce different levels of reinforcement corrosion, a calibration curve establishing a relationship between the duration of the impressed current and reinforcement corrosion was prepared. The magnitude of reinforcement corrosion was measured as gravimetric loss in weight of the steel bars. The results indicate a sharp reduction in the ultimate flexural strength of slabs with an up to a 29% reinforcement corrosion; thereafter, the strength decreased at a somewhat reduced rate with further increase in reinforcement corrosion. The ultimate deflection of the slabs decreases with an increase in the magnitude of reinforcement corrosion, leading to a marked and progressive reduction in the ductility of the slabs. Furthermore, the strength of plain-concrete slabs and those reinforced with steel bars of less than 60% corrosion was almost similar.

This paper presents test results obtained from studies aimed at determining whether the impact-echo method, a nondestructive test technique based on the use of transient stress waves, can be used to trace the initiation and propagation of cracks in composite slabs subjected to static loads. The number of shear studs in the specimens was designed to satisfy the requirement of the American Institute of Steel Construction Allowable Stress Design (ASD) specifications for full-composite and 80% partial-composite structures. To trace the initiation and propagation of cracks in the specimens, impact-echo tests were carried out at steps with different load levels. Throughout the test, the strains of shear studs were also measured to verify the results obtained from the impact-echo tests. It is shown that changes in the impact-echo responses are the key to detecting the formation of a crack in the composite slabs. The location of the crack can be determined by the impact-echo method. Results also show that the strains of shear studs start to have sharp increases after the applied load corresponding to the presence of cracks. Besides the conventional measurement devices, this study successfully introduces a newly developed nondestructive technique used for detecting cracks in concrete specimens to add valuable information to experimental results for better interpretation of structural failure mechanism.

In this paper, a comprehensive study of structural evaluation methods for jointed concrete airfield pavements is presented. A specially prepared concrete test pavement, consisting of six slabs with different size voids beneath the slabs at corners incorporated by variably spaced dowel joints, is loaded by the falling weight deflectometer (FWD) test system. By analyzing these FWD measurements with the finite element model, the usefulness of the FWD as a tool for measuring various important pavement properties is assessed. Based on the deflection basins measured by FWD, the resilient modulus of the foundation can be calculated, load transfer efficiency at joints of pavement can be determined, and the size of voids beneath the slab can be detected. Field measurements made at an in-service airfield pavement indicate that the FWD is a suitable device for the structural evaluation of jointed concrete airfield pavements.

Nine full-scale tests are described in which composite beams containing web holes are studied in an attempt to understand the mechanisms by means of which the slab participates in carrying vertical shearing force. In particular, the test evidence is examined for support of a truss analogy in which shear studs are considered as vertical tension members, and diagonal compression struts act in the concrete. Parameters investigated include stud configurations, the width of the concrete slab, and detailing of the studs in the hole region. The latter details are varied based on expectation of improved performance deduced from consideration of the truss analogy. Strength predictions are made by the truss analogy, described in a companion paper, and also based on previously published analyses, and test results are summarized for a total of 44 tests collated from many sources. Good agreement between observed and predicted failure loads is demonstrated for both theories. The truss analogy enables a clearer understanding of the slab behavior.

The load-carrying mechanism in concrete slabs of composite beams at web holes is studied. Using a truss analogy, the shear studs in the hole region are considered as vertical tension-carrying members, and inclined struts in the concrete are considered to act between bearing zones at the heads of the studs and at their bases at the steel beam flange. The structural action between the concrete slab and the shear connectors is clearly identified, and rational truss idealizations for determination of the slab shear-carrying capacity are developed. This approach relates the shear capacity to the location of studs, and three idealizations are used to provide solutions for three typical stud configurations. In this way, the ultimate resistance of composite beams containing large web holes is estimated. Both solid slabs and ribbed steel deck-supported slabs are considered.

A series of six full-scale subassemblages were tested to investigate dogbone and haunch retrofits for pre-Northridge steel moment connections. Tests included matched pairs of specimens, one bare steel and one including composite slab. Data were collected to evaluate the influence and behavior of the concrete slab. Results that emphasize the influence of the composite slab on connection behavior and specific comments on the slab response are presented. The presence of a composite slab corresponded to higher-achieved overall plastic rotations and higher-peak attained moments. Existing estimates of composite beam capacity overestimated the specimen strengths in positive moment. Shear stud failures were observed, raising concerns about the capacity of shear studs under severe reversed cyclic loading.

The moisture dome test is an effective method to determine the moisture content in a concrete slab which may cause damage to linoleum floor tiles. This test involves measuring the vapor flow rate at various slab locations and at different times of the year. The test apparatus consists of a plastic cover and an anhydrous calcium chloride preweighed dish. Moisture from the concrete slab is absorbed by the calcium chloride and the weight gained is then used to calculate the vapor flow rate.