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This research's primary objectives were first to verify a reliable structural health monitoring (SHM) experimental technique for reinforced concrete slab plates, and secondly, to introduce a special fiber Bragg grating (FBG) sensors cable system for continuous field monitoring of concrete. The particular focus was on the damage assessment, using an effective ambient vibration-based damage diagnostic technique of random decrement (RD). An investigation examined the extent of damage induced by progressive static loading through a numerical RD algorithm for four concrete plate specimens: three reinforced high-strength concrete (HSC) plates with different reinforcement ratios, and one ultra-high-performance fiber-reinforced concrete (UHP-FRC) plate. The extent of damage was measured through relative changes in the natural frequency and damping ratio as dynamic parameter damage indexes, which were obtained from RD signatures at cracking, yield, and ultimate loadings. Concurrently, the behavior of the concrete slabs was examined regarding the load-deflection relationship at service and ultimate load, crack pattern, and failure modes. [ABSTRACT FROM AUTHOR]

A numerical model is developed to predict the splitting and cracking stresses caused by bond action between the deformed bars and surrounding concrete of concrete specimens reinforced in both directions. This model considers the influence of confinement provided by the tensile strength of concrete cover and the transverse reinforcing bars perpendicular to the direction of the splitting cracks' propagation. Furthermore, this investigation is extended to provide design equations for evaluating the tensile strength of normal- and high-strength reinforced concrete (RC) plates subjected to a biaxial loading condition, considering the secondary effect of the splitting stress. The comparison between the predicted results of bond stresses, the concrete tensile strength, and the corresponding measured data obtained experimentally reveals a favorable agreement. [ABSTRACT FROM AUTHOR]

A strut-and-tie model is developed to model the punching shear behavior of thick concrete plates. This model provides a quick and simple approach to punching shear behavior. It is applicable to both normal- and high-strength concrete under symmetric and nonsymmetric loading with and without shear reinforcement. The strut-and-tie model for symmetric punching consists of a "bottle-shaped" compressive zone in the upper section of the slab depth, leading to a "rectangular-stress" compressive zone in the lower section depth. An equation based on failure criteria for the strut-and-tie method is used to model the behavior in the lower compressive stress zone. Another strut-and-tie model is also developed to rationally model nonsymmetric punching shear behavior due to unbalanced moment transfer and symmetric punching behavior of concrete slabs with shear reinforcement. The results of the strut-and-tie models for symmetric and nonsymmetric loading with and without shear reinforcement were compared to experimental test results performed and published by others. The results of the strut-and-tie models showed excellent agreement with available test results. [ABSTRACT FROM AUTHOR]

An experimental program was conducted recently at the Memorial University of Newfoundland (MUN) to study the tension-stiffening and cracking behavior of orthogonally reinforced concrete panels subjected to axial tension. The experimental program involved testing eight reinforced concrete panels with different concrete strengths under uniaxial or biaxial tension loading. During the duration of the tests, applied loads, strains, and crack widths were recorded. The average stress-strain relationship and crack width for concrete panels under direct tension were examined at different steel stress levels. The main objectives of this paper are to investigate the cracking behavior and tension-stiffening response of axially loaded high-strength reinforced concrete (HSC) panels and compare this behavior with the normal-strength concrete (NSC) panels. Based on the test results, a model is recommended for predicting the tensile stress-strain relationship of HSC panels under axial loading. [ABSTRACT FROM AUTHOR]

Thick concrete plates are currently used for offshore and nuclear containment concrete walls. In this research, five thick concrete slabs with a total thickness of 300 to 400 mm (12 to 16 in.) were tested under concentric punching loading. Four specimens had no shear reinforcement, whereas the remaining one included T-headed shear reinforcement consisting of vertical bars mechanically anchored at the top and bottom by welded anchor plates. The main focus of this research was to investigate the influence of the size effect on the punching shear strength of thick high-strength concrete plates. All tests without shear reinforcement exhibited brittle shear failures. The addition of T-headed shear reinforcement with a shear reinforcement ratio of approximately 0.68% by volume changed the failure mode to ductile flexural failure. The test results revealed that increasing the total thickness from 350 to 400 mm (14 to 16 in.) resulted in increased punching capacity and at the same time resulted in a small increase in ductility characteristics. An equation based on fracture mechanics principles is recommended to account for the size effect factor. The proposed equation is verified using the test results and is compared with the predictions of different design codes. [ABSTRACT FROM AUTHOR]

With the extensive use of thick concrete plates for offshore platforms and nuclear containment structures, the empirical building codes formulas for minimum flexural reinforcement ratios seem to provide excessive reinforcement. The current research has a main objective to establish experimental data for minimum reinforcement of normal-strength concrete (NSC) and high-strength concrete (HSC) plates with a thickness of 200 mm (8 in.) and greater. Ten full-scale quarter panels, NSC and HSC slab-column connections having small ratios of flexural reinforcement, were tested under flexural loading. The main test variables included concrete compressive strength, reinforcement ratio, and slab effective depth. ACI 318-08 does not contain a size effect factor; the new formula to calculate the minimum flexure reinforcement for thick HSC plates suggested by the authors was examined. Based on the experimental test results, it was concluded that ACI 318-08 overestimates the minimum reinforcement ratio required for thick concrete slabs greater than 200 mm (8 in.). [ABSTRACT FROM AUTHOR]

This research is focused on evaluating the crack widths and crack properties of thick two-way slabs and plates used for offshore and nuclear containment structures. The crack width depends on the quantities, orientation, and distribution of reinforcing steel across the crack and characteristics of the bond between the concrete and reinforcement bars in and near the crack. The maximum crack width that is considered acceptable depends on the type of structure, location within the structure, environment, and consequences of excessive cracking. A comprehensive experimental and analytical investigation is presented in this work. The numerical investigation will focus on the available code prediction models for estimating the crack width of concrete plates. The investigation will focus on the suitability of available crack width expressions for thick concrete plates used for offshore concrete structure applications and nuclear containment structures. The experimental work included the investigation of the cracking behavior, such as examining the effect of increasing concrete cover and bar spacing on crack width properties. The crack widths were measured electronically for three series of specimens. The test results were tabulated to compare test results with the available code expressions for calculating crack widths. The tension chord method was modified to predict the crack width for two-way plates under flexural loading. [ABSTRACT FROM AUTHOR]

Different codes have different formulas to calculate crack spacing and crack width developed in flexural members. Most of these formulas are based on the analysis of results of tested beams or one-way slabs. Crack control equations for beams underestimate the crack width developed in plates and two-way slabs. It seems that little attention has been paid in determining the crack spacing and width in reinforced concrete plates. The behavior of reinforced concrete plates and two-way slabs is different from beams or oneway slabs; therefore, the methods developed for beams cannot be directly applied to plates and two-way slabs. In this paper, a new analytical equation is proposed for calculating the crack spacing for plates and two-way slabs. A special focus will be given to thick concrete plates used for offshore and nuclear containment structures. The proposed equation takes into account the effect of steel reinforcement in the transverse direction through the splitting bond stress. The new equation provides good estimates for crack spacing in plates and two-way slabs with different concrete covers. Eight full-scale two-way slabs were designed and tested to examine the effects of concrete cover and bar spacing of normal- and highstrength concrete on crack spacing. The different code expressions are evaluated with respect to the experimental results. [ABSTRACT FROM AUTHOR]

Most concrete codes have empirical equations to estimate the minimum steel reinforcement requirements for flexural members. High-strength thick concrete plates are used for offshore and containment structures for nuclear power generation. An accurate estimate of the minimum steel flexure reinforcement ratio can result in saving millions of dollars for a single project. The recommended concept utilizes the fracture mechanics principles to modify the sandwich panel model and account for thick slabs. A comparison between the proposed equations with experimental tests carried by Battista is conducted; also, a comparison of the proposed equation with different code formulas is illustrated. The results obtained by the proposed equations are confirmed by the Norwegian code (NS 3474E) and suggestions by Bosco and Carpinteri. In summary, the two new main contributions in this research are as follows: the first contribution considers the size effect through fracture mechanics, and the second contribution considers the torsional moment for thick plates in calculating the minimum reinforcement of thick plates. [ABSTRACT FROM AUTHOR]

Future construction of concrete floating platforms for offshore oil exploration off the east coast of Canada will lead to a substantial increase in the use of high-strength lightweight (HSLW) concrete. HSLW concrete has been extensively used in Norway and other parts of Europe. HSLW concrete with its high durability and lightweight characteristics is a very much sought after material in the construction of concrete floating platforms. The main objective of this investigation is to determine the bond strength characteristics of HSLW concrete. The experimental program consisted of testing 72 pull-out and push-in specimens to evaluate the bond behavior under monotonic and cyclic loading using 25 and 35 mm (No. 8 and No. 11) deformed reinforcement embedded in high strength of 80 MPa (11.6 ksi) lightweight concrete. The static and cyclic test results indicated that HSLW concrete behaves very similar to high strength normalweight concrete. The bond strength of HSLW was equal to or slightly larger than similar specimens made of high strength normalweight concrete (HSNW) at the same lab. The bond stress versus displacement curve indicated a sharp linear ascending portion followed by a steep descending portion indicating a brittle failure, which is characteristic of high-strength concrete. The ACI 318 code increases the minimum development length of lightweight concrete by 30%. The ACI recommendation of this increase is unjustified for high-strength concrete made of lightweight aggregates. [ABSTRACT FROM AUTHOR]

In this paper, the strengthening of two-way slabs using fiber-reinforced polymers (FRPs) is evaluated experimentally. Two different types of FRP materials were evaluated: carbon FRP strips and glass FRP laminates. The dominating failure mode for two-way slab, flexural, or punching shear is based on the slab steel reinforcement ratio. The reinforcement ratios were chosen to serve the purpose of demarcating the two possible modes of failure. The tested specimens were classified according to the purpose of strengthening into specimens strengthened in flexure and specimens strengthened in punching shear. Specimens strengthened in flexure had two steel reinforcement ratios: 0.35 and 0.5%. Results show that the flexural capacity of two-way slabs can increase to an average of 35.5% over that of the reference (unstrengthened) specimen. An increase of the initial stiffness was achieved for flexural specimens; however, an apparent decrease in the overall ductility was evident. FRP materials can be used to increase the flexural capacity of two-way slabs. However, an average decrease in the values of the energy absorption of approximately 30% for flexural strengthening specimens was observed. Specimens strengthened for punching shear have an original slab reinforcement ratio of 1.0%. A strengthening technique that combines the use of carbon FRP strips and steel bolts increases the strength of the slab by 9.0%. An analytical model for the analysis of FRP strengthening of two-way slabs under flexure or punching shear is introduced. [ABSTRACT FROM AUTHOR]