Behavior Of Concrete Slabs Research Articles

Smoothed particle hydrodynamics versus finite element method for blast impact

Abstract The paper considers the failure study of concrete structures loaded by the pressure wave due to detonation of an explosive material. In the paper two numerical methods are used and their efficiency and accuracy are compared. There are the Smoothed Particle Hydrodynamics (SPH) and the Finite Element Method (FEM). The numerical examples take into account the dynamic behaviour of concrete slab or a structure composed of two concrete slabs subjected to the blast impact coming from one side. The influence of reinforcement in the slab (1, 2 or 3 layers) is also presented and compared with a pure concrete one. The influence of mesh density for FEM and the influence of important parameters in SPH like a smoothing length or a particle distance on the quality of the results are discussed in the paper

Strain Behaviour of Concrete Slabs under Impact Load

This paper presents drop tower experiments. In order to analyse the behaviour of concrete slabs under high strain rates, an impact mass is dropped from a maximum height of 9 m onto square concrete slabs with a side length of 1 m. Slabs of different concrete strengths are tested and the behaviour of standard concrete slabs is compared to that of high performance concrete (HPC) and ultra-high performance concrete (UHPC). Furthermore, the influence of an additional strengthening layer of fabric reinforcement is analysed. For this, steel cord fabric and carbon cord fabric are applied to a slab group. The concrete strain on the slab top and the steel strain on the slab bottom are monitored. Based on the analysis of the concrete strain and the steel strain, the local behaviour and global behaviour due to the impact load can be identified. In addition to the measurement results, slab perforation and damage effects due to impact load are evaluated qualitatively. Comparing the concrete specimen with and without additional fabric strengthening, substantial advantages in the resistance to the impact load and to the penetration of the impactor are seen for slabs with a strengthening layer.

Experimental Study on Bending Behavior of Concrete Slabs Reinforced by Cold-Rolled Ribbed Steel Wires with Improved Elongation

Cold-rolled ribbed steel wires with improved elongation is a new type of cold-rolled steel wires, this paper presents the test results of 6 concrete slabs reinforced by the cold-rolled ribbed steel wires with improved elongation under flexure, the flexural characteristics, bearing capacity, deflection and cracking of these slabs under loading are analyzed, the formulas for calculating the flexural bearing capacity, the deflection and crack width of the slabs are suggested. This may be as a reference for the applications of this new type of cold-rolled steel wires, and for the revision of Chinese Code Technical specification for concrete structures with cold-rolled ribbed steel wiresJGJ95-2011.

Punching shear strength of steel fibre reinforced concrete slabs

The ultimate strength of reinforced concrete slabs is frequently governed by the punching shear capacity, which may be increased with addition of traditional fitments such as reinforcing steel, headed studs or shear heads. In addition to these traditional methods of strengthening against punching, steel fibre reinforcement has proved to be an effective and viable alternative. The addition of fibres into the concrete improves not only the shear behaviour but also the deformation capacity of reinforced concrete slabs. This paper presents a mechanical model for predicting the punching strength and behaviour of concrete slabs reinforced with steel fibres as well as conventional reinforcement. The proposed model is validated against a wide number of available experimental data and its accuracy is verified. On this basis, a simple design equation for the punching shear capacity of steel fibre reinforced concrete (SFRC) slabs is proposed.

Design of Thick Concrete Plates Using Strut-and-Tie Model

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.

An Experimental Study of the High Temperature Behavior of Concrete Slabs Strengthened with Carbon Fiber Reinforced Polymer (<i>CFRP</i>) with Inorganic Adhesive

Nowadays the mechanical properties of epoxy resin used to paste CFRP strengthening the concrete structures, has a sharp drop in more than 60°C. Four CFRP-strengthened concrete one-way slabs were studied in the fire, one using epoxy resin and the other three using inorganic adhesive (Magnesium Oxychloride Cement). The experimental results show that :(a) The fire resistance performance of CFRP-strengthened concrete slab by inorganic adhesive with 15mm thickness fire protection was better than the slab without fire protection; (b) Without considering the impact of burst, the fire resistance performance of CFRP-strengthened concrete slab by inorganic adhesive with 30mm fire protection was better than the slab with 15mm fire protection;(c)Under the same fire protection measures, the fire resistance performance of CFRP-strengthened concrete slab with inorganic adhesive was better than the concrete slab strengthened with CFRP by epoxy adhesive.

Composite Behavior of Concrete Slab with Steel Decking under Flexural Loading

In this study, mechanical behavior and failure pattern of composite concrete deck were investigated. A unique dimension of steel concrete deck was fabricated and tested in four-point bending. Two series of decking were also designated with bolts at a spacing of 15 cm and 30 cm, used to compare with those without bolt. Totally, 9 composite concrete decks were tested in a close-loop servo-hydraulic testing system (MTS) using displacement control. Load versus displacement curves as well as failure patterns of the specimens were studied to figure out the mechanical behavior of this type of composite structure.

Investigation of Concrete Slabs under Impact Load

The behaviour of concrete slabs under dynamic load such as rock fall or vehicle impact isinvestigated in this work. The aim of this study is to enlarge the knowledge concerning thesubsequent reinforcing of concrete slabs and its inuence on their behaviour under impact load.Therefore, the results of the drop tower experiments with standard concrete, high performanceconcrete (HPC) and ultra-high performance concrete (UHPC) are compared and interpreted.The analysis of the test results focuses on the qualitative evaluation of the protective e ectand on the quantitative evaluation of measurement results. Regarding the protective e ect, theinuence of the additional steel stirrup reinforcement is rather small. In contrast, the subsequentfabric reinforcement prevents the perforation of the concrete slabs. The behaviour of steel fabricand carbon fabric is compared. Although particular di erences in fracture behaviour are seen,both types of fabric reinforcement obviate total punch-through and, hence, vastly enhance theprotective performance. Comparing the stamping cones and analysing the extent of damage, theprotective capacity of di erent concrete slabs is evaluated. Within the quantitative evaluationof the measurement results, the evolution of strains and strain rates is being considered. Onthe top side of the concrete slabs, the strain is measured as tensile strain in the rst spellafter load application, turning into compressive strain later on. The evolution of strains andstrain rates indicates wave propagation. Beside the strain results, special attention is paid tothe correlation of di erent measurement techniques. The results of strain gauges, accelerometer,load cells and photogrammetry are contextualised and therefore show the change from the localmaterial behaviour to the global structure response in temporal sequence.

Fire resistance of concrete slabs reinforced with FRP bars. Part II: Experimental results and numerical simulations on the thermal field

Use of fiber reinforced polymer (FRP) bars or grids instead of traditional steel reinforcements is an interesting application, especially to improve structural durability and extend the actual service life. As proved elsewhere by experimental and numerical results, a key aspect of the structural behavior of concrete slabs reinforced with FRP bars is the large reduction in both resistance and stiffness due to high temperatures. Thereupon six concrete slabs reinforced with glass FRP bars characterized by different values of concrete cover and anchorage length were recently tested in the fire situation. A comprehensive description of the experimental program and some significant experimental results are reported in a companion paper; the resistance of concrete slabs reinforced was showed strongly influenced by temperatures in the bars in the area directly exposed to fire but also in the anchoring area (not exposed zone). In this paper, at first, a detailed discussion of the experimental thermal readings is reported to give as a support to the remarks on mechanical response of the slabs reported in the companion paper. In particular the influence of concrete cover on temperature in exposed area and the temperatures in the area not exposed are examined to investigate the effectiveness of the anchor. The influence on the temperature in the bars of different concrete thermal properties is investigated. Furthermore, the influence of the thermal properties of the bars on the temperature field is evaluated. Finally, a simplified method for predicting temperatures of FRP bars in concrete slabs, obtained by considering the ISO standard fire curves is provided in the form of analytical relationships .Its reliability is showed by means of comparisons with the experimental results.

Improved methods for decreasing stresses of concrete slab of large-span through tied-arch composite bridge

Mechanical behavior of concrete slab of large-span through tied-arch composite bridge was investigated by finite element analysis (FEA). Improved methods to decrease concrete stresses were discussed based on comparisons of different deck schemes, construction sequences and measures, and ratios of reinforcement. The results show that the mechanical behavior of concrete slab gets worse with the increase of composite regions between steel beams and concrete slab. The deck scheme with the minimum composite region is recommended on condition that both strength and stiffness of the bridge meet design demands under service loads. Adopting in-situ-place construction method, concrete is suggested to be cast after removing the full-supported frameworks under the bridge. Thus, the axial tensile force of concrete slab caused by the first stage dead load is eliminated. Preloading the bridge before concrete casting and removing the load after the concrete reaching its design strength, the stresses of concrete slab caused by the second stage dead load and live load are further reduced or even eliminated. At last, with a high ratio of reinforcement more than 3%, the concrete stresses decrease obviously.

The behaviour of reinforced concrete slabs in fire

In this paper a robust model is presented based on the previous layer procedure developed by the author to also take into account the effects of concrete spalling on the behaviour of concrete slabs under fire conditions. In this study, a detailed analysis of a uniformly loaded reinforced concrete slab subject to different degrees of concrete spalling under a standard fire regime is first carried out. Further, a series of analysis of floor slabs with different degrees of concrete spalling is also performed on a generic reinforced concrete building. A total of 16 cases have been analysed using different degrees of spalling on the slabs, with different extents and positions of localised fire compartments. It is clear that adjacent cool structures provide considerable thermal restraint to the floor slabs within the fire compartment. And it is evident that the compressive membrane force within the slabs is a major player in reducing the impact of concrete spalling on the structural behaviour of floor slabs in fire.

Shear Behavior of Concrete Slabs Longitudinally Reinforced with High-Performance Steel

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Erratum to “Flexural behavior of concrete slabs with corroded bars” [Cement & Concrete Composites 30(3) (2008) 184–193

Erratum to “Flexural behavior of concrete slabs with corroded bars” [Cement & Concrete Composites 30(3) (2008) 184–193

Comments on “Flexural behavior of concrete slabs with corroded bars”

This paper presents a discussion on a paper authored by Chung et al. [Chung L, Najm H, Balaguru P. Flexural behaviour of concrete slabs with corroded bars. Cement Concr Compos 2008;30:184-93].

Flexural behavior of concrete slabs with corroded bars

Experimental and analytical evaluations of concrete slabs reinforced with corroded and uncorroded bars are presented. Seventy simply supported slabs reinforced with 10 mm diameter bars were tested in bending using a four-point load setup. The primary variables were the bond length and the corrosion level. The bond lengths varied from 10 to 440 mm and corrosion levels ranged from 0% to 4.6% diameter loss. The moment capacity of the slabs was also predicted using results from pull-out tests conducted on corroded bars in a separate study. The results indicate that the behavior of the slabs with corroded reinforcement can be predicted with good accuracy. As in the case of pull-out tests, a small amount of corrosion increases the flexural capacity of the slab. But the capacity reduces considerably when the loss in bar diameter exceeds 2%. The results confirm the hypothesis that bond deterioration is the major contributor to the reduction of moment capacity.

Tension-stiffening model for FRP-strenghened RC concrete two-way slabs

The main focus of this paper is to present a tension-stiffening model that is suitable for finite element analysis (FEA) aimed at investigating the effect of FRP strengthening on the tensile behaviour of concrete slabs. Available experimental results of the FRP-strengthened reinforced concrete slabs are used to calibrate the finite element model based on the ultimate load carrying capacity of the two-way slabs. The proposed tension-stiffening model is implemented into the constitutive concrete model defined in a general-purpose finite element code. Reinforced concrete behaviour in tension can signifcantly be changed due to strengthening. An overall increase in the post-peak stiffness based on the tensile stress-strain relationship is observed. A simplified bilinear model is introduced to define the behaviour of the FRP-strengthened concrete in tension. An expression of the fracture energy density is introduced to define the area under the concrete tensile stress-strain relationship. The tensile stress-strain relationship of concrete is referred to as the tension-stiffening model. It is shown numerically that the ultimate load capacity of two-way slab specimens is sensitive to the fracture energy density. Hence, a distinction has to be made between the definitions of the tension-stiffening model of FRP-strengthened and un-strengthened concrete. This distinction is the focus of this paper.

Behavior of concrete slab under frictional drag

Concrete pavement slabs experience volume change due to the variation of temperature and moisture level. The frictional drag acting on the bottom of slab due to the base friction is in the opposite direction of horizontal slab displacement, and resist against the horizontal slab movements. The magnitude of frictional force and horizontal slab displacement has interdependent relationship. A mechanistic analysis tool (SSM Program) is introduced to study the behavior of concrete slab under frictional drag, with accounting for the interdependent relationship between horizontal slab displacement and frictional drag. Also, potential factors affecting behavior of concrete slab under frictional drag, including base type, slab length, and temperature range are investigated.

Behaviour of Composite Bridges during Construction

The behaviour of steel-concrete composite bridges is influenced by time-dependent effects in the concrete deck slab that can affect the durability of such structures. A detailed study of the causes of transverse cracking in concrete slabs of composite bridges has been carried out to understand better the origin of tensile stresses in the slab. In situ measurements and laboratory tests have enabled the behaviour of concrete slabs to be observed from the moment they were placed. The results demonstrate the important influence of concrete hydration and the pouring sequence on the tensile stresses in the slab. It is shown that for typical bridges the most critical tensile stresses in the slab are induced during construction. Methods for limiting the effects of hydration have been tested and the results compared with those of numerical simulations. A criterion for evaluating the probability of crack formation in young concrete has been established based on these simulations.

Nonlinear analysis of steel–concrete composite beams curved in plan

This paper deals with the behavior of structural steel–concrete composite beams curved in plan. The finite element package ABAQUS has been used to study the nonlinear behavior and ultimate load-carrying capacity of such beams. A three-dimensional finite element model has been adopted. Shell elements have been used to simulate the behavior of concrete slab and steel girder, and rigid beam elements to simulate the behavior of shear studs. The proposed finite element model has been validated by comparing the computed values with available experimental results. An acceptable correlation has been observed between the computed and experimental results obtained for beams of realistic proportion.

A neural network approach for predicting the structural behavior of concrete slabs

In this paper the use of a nontraditional technique, neural networks, has been investigated as a means to develop efficient predictive models of the structural behavior of concrete slabs. The applicability of neural networks within the realm of structural analysis is first reviewed, along with their state-of-the-art applications and research efforts. Four neural networks have then been developed to model the load-deflection behavior of concrete slabs, the final crack-pattern formation, and both the reinforcing-steel and concrete strain distributions at failure. The four neural networks were trained and tested using the experimental results of 38 full-scale slabs. Details regarding data modeling, neural network training, and performance evaluation are described. Using the developed networks, a spreadsheet tool for the structural analysis of concrete slabs was developed with a simple interface, automated predictions, and what-if capabilities. The developed tool is useful for teaching purposes and for reasonable prediction of the behavior of concrete slabs without additional experimental testing.Key words: neural networks, structural analysis, reinforced concrete, load-deflection, crack pattern, artificial intelligence, concrete slabs.