Concrete Slab Thickness Research Articles

Study on mechanical behavior of rockfall impacts on a shed slab based on experiment and SPH–FEM coupled method

The mechanical behavior of rockfall impacts on shed slabs was studied in three aspects: the rockfall impact force, the inertia effect coefficient, and the structural damage evaluation. A test model composed of a concrete slab and a cushion layer was constructed. Nine batches of impact experiments with energies ranging from 50 to 250 kJ were conducted. The dynamic impact model was established using LS-DYNA to analyze the dynamic impact response characteristics and inertia effect based on the SPH–FEM coupled method. Moreover, random sample expansions were calculated, and methods for assessing the impact force and inertia effect coefficient were proposed. In addition, the applicability of the proposed equation was verified by comparing the calculated results with relevant published experimental data and the Japanese calculation method of impact force. Furthermore, the velocity and mass of the rockfall were selected as the main control variables for damage assessment. A damage assessment index based on punching bearing capacity was established, and the level of damage was classified. Additionally, the influence of the parameters of the concrete slab and cushion layer thickness on damage assessment was analyzed. The impact resistances of the Ultra-High Performance Concrete (UHPC) and normal concrete slab were compared. The results demonstrated that the effect of impact force and the concurrent impact-induced inertia effect should be considered in structural designs. The larger the mass rockfall, the greater the damage sustained by the slab under the same impact energy. The compressive strength of concrete and the yield strength of steel have the greatest and least influence on the damage degree, respectively. A 90 cm-thick sand cushion on a slab increases the impact resistance of the slab by 25%–30%, compared with a 60 cm-thick sand cushion layer. Moreover, it was found that the UHPC concrete slab has good impact resistance, which is approximately twice that of the C40 concrete slab. One of the highlights in this paper is that the SPH–FEM coupled method is proposed to reproduce the physical phenomenon of sand pit-forming. Compared with FEM, SPH–FEM generates a simulated value that is closer to the experimental value.

Experimental and numerical study on the in-plane behaviour of a new long-span assembly composite floor system under lateral load

ABSTRACT A new long-span assembly composite floor system for use in multi-column frame-tube structure is presented. The basic assembly unit consists of steel truss keel and profile sheet concrete composite slab, which of the two parts are combined together through shear stud. By means of standardized assembly connection structure, such a new floor system can realize a rapid assembly of floor and support frame. Based on test research of 1/3 scale model, the paper discusses the in-plane mechanical performance of the new floor system. Through loading at the direction of parallel to the assembly slab seam and perpendicular to the assembly slab seam, respectively, the influence of assembly orientation of floor units on the failure modes, distribution and transmission performance of the horizontal loads, and the in-plane stiffness were identified in detail. A numerical model was developed with its input parameters calibrated from full-scale experimental tests. Based on model analysis, the influence of thickness of concrete slab on the in-plane stiffness was discussed.

ANALYSIS OF THE EFFECT OF SLAB THICKNESS ON CRACK WIDTH IN RIGID PAVEMENT SLABS

Cracks that occur in rigid pavements include longitudinal cracks, transverse cracks, and corner cracks. The relatively large crack width not only spoils the aesthetics of the concrete structural elements but can also lead to structural failure. This study aims to determine the crack width of a rigid pavement concrete slab located above the subgrade which is considered a beam on an elastic foundation, so that a minimum rigid pavement concrete slab thickness can be recommended. The specimen will be observed at various thicknesses to obtain the optimum thickness. The load used is a centralized monotonous load, which represents the load of the truck vehicle. The research limitation is using a test object in the form of a concrete plate measuring 2000x600 mm which is placed on the ground with CBR=6 %. The quality of reinforced concrete slabs is fc'=40 MPa and fy=440.31 MPa. The thickness of the concrete slab varies between 100 mm, 150 mm, and 200 mm. The slab placed on the ground is then given a central loading in the form of a centralized monotonic load. The loading range starts from a load of 2–180 kN with a load interval of 2 kN. The experimental results show that the rigid pavement slab has a bending failure so that the crack pattern that occurs begins with the first crack on the underside of the slab. The crack pattern in terms of slab thickness variation has a similar pattern. The initial crack width on the slab is 0.04 mm. The thicker the slab smaller the crack width at the same load. Based on the maximum allowable crack width=0.3 mm. For loads between (80–100) kN (Road Class I, II, and III), a minimum thickness of rigid pavement slabs (70–80) mm is recommended. For loads between (130–140) kN, the minimum thickness of the rigid pavement slab (105–115) mm is recommended

Experimental and analytical study of the shear strength and stiffness of studs embedded in high strength concrete

Push-out test was carried out to investigate the influence of the ratio of the stud height to the concrete slab thickness and the reinforcement layout on the shear performance of the headed stud embedded in high strength concrete (HSC). Test results indicated that the influence of the ratio of stud height to concrete slab thickness on the shear stiffness should be taken into consideration. A shear stiffness prediction formula, which has clear physical meaning and simple expression, was proposed and validated. The predicted shear stiffness by the proposed equation is in good agreement with experimentally determined value. According to this formula, the shear stiffness of studs is affected by the stud diameter, compressive strength and elastic modulus of HSC. In addition, a formula to predict the shear strength of a stud embedded in HSC considering both the interaction between stud and concrete and the enhancement effect of the welded collar was also proposed and evaluated. The mean ratio of predicted results obtained from the proposed formula to experimental results is 0.98.

Behaviour of steel–concrete composite girders under combined negative moment and shear

Existing studies on the behaviour of steel–concrete composite girders under combined bending and shear are mainly focused only on composite beams with compact sections; very few studies have investigated slender composite girders, which are commonly used in bridge engineering. Therefore, the behaviour of slender steel–concrete composite girders under combined negative moment and shear were investigated experimentally and numerically in this paper. With the moment/shear ratio, reinforcement ratio, connection type, and web thickness as the experimental parameters, experiments were conducted on seven simply supported composite girders subjected to negative moment and shear. The test results showed that reinforcement ratio, concrete slab thickness, and web thickness significantly influence the ultimate load and failure modes of composite girders; the connection type only slightly influences the behaviour of full-shear-connection composite girders under combined negative moment–shear interaction. All the test data were outside the moment–shear interaction curve of Eurocode 4, i.e. Eurocode 4 tended to produce safer results. Then, a nonlinear finite element model was developed and validated using the experimental results. The factors affecting the moment–shear interaction of composite girders in negative-moment zones were studied through numerical simulation. The numerical results showed that the negative moment–shear interaction law changes little with the change of reinforcement ratio or slab thickness. The web depth-to-thickness ratio significantly influences the negative moment–shear interaction law, and the higher the web depth-to-thickness ratio, the earlier the composite girder begin experiencing moment–shear interaction.

Analysis of shear lag effect in the negative moment region of steel-concrete composite beams under fatigue load

Shear lag effect was a significant mechanical behavior of steel-concrete composite beams, and the effective flange width was needed to consider this effect. However, the effective flange width is mostly determined by static load test. The cyclic vehicle loading cases, which is more practical, was not well considered. This paper focuses on the study of shear lag effect of the concrete slab in the negative moment region under fatigue cyclic load. Two specimens of two-span steel-concrete composite beams were tested under fatigue load and static load respectively to compare the differences in the negative moment region. The reinforcement strain in the negative moment region was measured and the stress was also analyzed under different loads. Based on the OpenSees framework, finite element analysis model of steel-concrete composite beam is established, which is used to simulate transverse reinforcement stress distribution as well as the variation trends under fatigue cycles. With the established model, effects of fatigue stress amplitude, flange width to span ratio, concrete slab thickness and shear connector stiffness on the shear lag effect of concrete slab in negative moment area are analyzed, and the effective flange width ratio of concrete slab under different working conditions is calculated. The simulated results of effective flange width are compared with calculated results of the commonly used specifications, and it is found that the methods in the specifications can better estimate the shear lag effect in concrete slab under static load, but the effective flange width in the negative moment zone under fatigue load has a large deviation.

The foam concrete temperature measuring during its microwave heat treatment

The actual problem of accelerating and reducing the energy costs of the foam concrete slabs heat treatment technological process is considered. It is shown that to solve this problem, it is advisable to use the microwave radiation energy as a heat source. The main advantages of the microwave method of foam concrete slabs heat treatment in comparison with traditional methods are considered. The design of a microwave installation for the foam concrete slabs heat treatment has been developed. The installed microwave radiation sources have energy outputs in the form of a rectangular waveguide openings, which are used as radiating antennas. Huygens-Kirchhoff method was used to calculate the temperature distribution on the foam concrete slab surface; the method of loaded long lines was used to calculate the temperature distribution over the foam concrete slab thickness. A method for measuring the foam concrete slab temperature distribution is proposed. The results of theoretical and experimental temperature distribution studies on the surface and the cross-section of foam concrete slab with a width of 1500 mm, a height of 1000 mm and a thickness of 200 mm, a density of 1000 kg/m3 on the electromagnetic fields oscillation frequency of 2450 MHz are shown. The obtained experimental results showed a high efficiency of using microwave radiation for the foam concrete slabs heat treatment technological processes. Microwave technologies can be used for heat treatment of products made of concrete, reinforced concrete and polymer composite materials.

Ballistic impact on concrete slabs: An experimental and numerical study

The ballistic perforation resistance of 50 mm thick concrete slabs impacted by 20 mm diameter ogive-nose steel projectiles is investigated experimentally and numerically. Three commercially produced concretes with nominal unconfined compressive strengths of 35, 75 and 110 MPa were used to cast material test specimens and slabs. After curing, ballistic impact tests were carried out to determine the ballistic limit curve and velocity for each slab quality. Material tests instrumented with digital image correlation (DIC) were conducted along the ballistic impact tests. DIC measurements were used to establish engineering stress-strain curves for calibration of a modified version of the Holmquist-Johnson-Cook concrete model. Finite element simulations of the impact tests gave good conservative predictions.

Dynamic Performance of Reinforced Concrete Slabs Under Impact and Blast Loading Using Plasticity-Based Approach

A plasticity-based approach has been proposed for reinforced concrete (RC) subjected to impact and blast loading. The proposed approach includes a new failure surface together with modified descriptions related to equation of state, strain rate effect and damage taken from literature. These selective descriptions in numerical analysis have been found to give better results than the existing models. A user-defined UMAT subroutine for the commercial software LS-DYNA has been developed for the proposed model. Dynamic analysis for both blast and impact type of loading on RC slabs are performed. The results are compared with an in-built material model in commercial software LS-DYNA, namely the Winfrith concrete model (WCM) and with experimental results taken from literature. A parametric study is carried out by analyzing the mechanical and damage response by varying parameters such as concrete strength, slab thickness and reinforcement ratio. The proposed approach is found to be effective in predicting the behavior under both impact and blast analysis.

Experimental investigation of the vertical shear performance of steel–concrete composite girders under negative moment

To investigate the vertical shear performance of steel–concrete composite girders commonly used in bridge engineering, experimental tests were conducted on five simply supported composite girders and one bare steel girder under negative moments. The main test parameters were depth and reinforcement ratio of concrete slab, connection type, and web thickness. The test results showed that the ultimate load of the composite girder increased by 10–20% compared with that of the bare steel girder. When the concrete slab thickness increased from 115 mm to 180 mm, the reinforcement ratio was doubled, web thickness increased from 6 mm to 8 mm, the shear capacity of the composite girders increased by 9.1%, 4.4%, and 49%, respectively. The specimen with Perfobond rib connectors exhibited comparatively better ductility. Compared with the results obtained with the current AASHTO and EC4 codes, the shear capacity increased by 8–16% and 5.8% for composite girders with web thicknesses of 6 mm and 8 mm, respectively. A nonlinear finite element model was developed and verified using the test results. Using the validated numerical model, the shear distribution of the cross-section was investigated and parametric analyses were conducted. The shear distribution of the section was divided into four stages, namely elastic, slab cracking, steady, and web buckling stages, during the entire loading procedure. Parameter analysis showed that the slab thickness significantly influences the shear capacity of the composite girder. With increasing web depth–thickness ratio, the contribution of the concrete slab to the shear capacity increases.

Structural Design of Prefabricated Sidewalk in Sponge City

In the traditional pavement design, rainwater is mainly discharged by surface runoff, and in the structural design, the key point is the pavement waterproof. Therefore, the traditional sidewalk design is inconsistent with the requirements of sponge city. The research basis of this paper comes from a field engineering, the structural parameters of prefabricated sidewalk and the corresponding design methods are studied and summarized. The structural function of sidewalk is realized by superposition and combination of each structural layer. For the realization of prefabricated sponge sidewalk technology, the function of each structural layer must be fully considered, and the function of each structural layer should be designed and combined according to the design purpose. The results show that, by discussing the function of each layer of prefabricated sidewalk, the structural layer of prefabricated sidewalk is preliminarily determined(see Figure 2 in main text); according to the strength requirements and water permeability requirements of the structure, the thickness range of the structural layer is 13.11cm-21.3cm; finally, the relationship between plate thickness and critical position load, temperature fatigue stress, and finally determines the thickness of precast cement concrete slab is 15cm.

Shear behavior of geocell-geofoam composite

In design, internal stability of EPS lightweight fills are provided either by applying load distributing mechanisms (thick pavements or concrete slabs) or using more strong lightweight material through denser EPS geofoam blocks. However, unit weight of the EPS geofoam is a limited parameter. As an attempt to improve the mechanical properties of EPS geofoam, geocell-geofoam composite (GGC) is introduced in this study. Geocell mattresses were infilled with solidified geofoam beads in the factory to fabricate GGC. The EPS geofoam and GGC samples were tested using a large-scale shear test apparatus of size measuring 1 m3. Results indicate that inclusion of the geocell leads to a considerable increase in the shear strength and a great decline in the compressibility of the geofoam. In comparison with EPS blocks, up to 72% rise in the shear strength and 67% decline in the vertical displacement were observed in GGC samples at the normal stress of 35 kPa. In addition, incorporation of the geocell was found to change the resisting mechanism of the EPS geofoam from cohesive to cohesive-frictional. While there was only 4.5% decline in the cohesion, the internal friction angle of the tested geofoam increased six-fold due to the involvement of the geocell.

Numerical simulation of reinforced concrete slab subjected to blast loading and the structural damage assessment

The structural dynamic response and failure behavior of reinforced concrete slab subjected to TNT blasts under different conditions are studied numerically. Three-dimensional finite element model with TNT, air and reinforced concrete slab was established, in which the reinforced concrete structure adopts the solid hexahedral separation common node modeling. Fluid-structure coupling algorithm combined with appropriate constitutive model and failure algorithm were used to analyze different explosion conditions. Intensive numerical simulations are carried out on different combinations of working conditions for TNT mass from 0.1 kg to 3.5 kg, blast distance from 100 mm to 800 mm, reinforced concrete slab thickness from 40 mm to 120 mm. Then, the relationship between the different explosion conditions and different damage levels (Low damage, Medium damage and Severe damage) of the reinforced concrete structure is established in this paper. In order to verify the numerical modeling and materials parameters, numerical simulation model validation is given, the results presents well the fracture and collapse of the reinforced concrete structure subjected to TNT blasts. Shock Wave's Peak Pressure data obtained by the numerical simulation is in good agreement with the prediction results of Henry's Formula. The results of reinforced concrete structural damage, including collapse radius and deflection, are in good agreement with the experimental phenomenon and data obtained by Wang et al. (2012).

Analytical Study on the Behaviour of Composite Space Truss Structures with Openings in a Concrete Slab

A space truss structural system is a three-dimensional arrangement of linear elements in a pyramid pattern forming a Double Layer Grid (DLG) system. Space trusses are an elegant and economical means of covering larger areas such as roof systems, in a wide variety of applications such as a stadium, aircraft-hanger, assembly hall, etc. The major problem encountered in using the space truss as a roofing system is the sudden failure of the whole structure due to critical buckling of the top chord member. Earlier research has shown that the optimal solution to overcome such a failure is by providing a small thickness of concrete slab over the space truss, so that the space truss with concrete slab (Composite Space Truss) will act as a floor system for the multi-storey building. For better ventilation and lighting in the building, the need for openings in the composite space truss is unavoidable; however, providing an opening in the concrete slab will reduce the load carrying capacity of the structure. The analysis of a composite space truss of size 30m x 30m with all possible locations of openings for four different support conditions was carried out using ANSYS in order to study the load - deflection behaviour. Further, the ductility factor and energy absorption capacity of the composite space truss with different locations of slab openings were compared.

Nonlinear 3D finite element modelling of conventional and composite steel spaceframes structures

Spaceframes steel structures are a common worldwide technique for roofing wide areas. In this study, after validating one of the models experimentally, nonlinear 3d finite element modelling were performed to analyze failure mechanism of space frames models with the help of Abaqus program. Additionally, this study attempts to convert such common roofing structure to a composite structure using ultra high strength concrete slab to withstand various floor loads. Various space frames shaft angles were tested, namely, 30, 45, and 60. Tests results were evaluated and compared in term of ultimate load, load at maximum displacement, toughness, and stiffness. Tests results have shown that spaceframes models with angle 60 have the highest load capacity compared to other angles, and highest toughness compared to various techniques. Also, compositing 40 mm of ultra-high-performance concrete slab method has approved its efficiency to withstand loads and showed comparable results with the conventional spaceframes. the composite systems with sufficient concrete slab thickness and strength have reflected an efficient technique for flooring wide span structures.

Shear stiffness of inclined screws in timber–concrete composite beam with timber board interlayer

The timber board interlayer is applied as the formwork for the pouring of concrete slab in various practical applications of timber–concrete composite structures, with the rehabilitation of timber buildings, in particular. At present, there are few studies performed to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. In this article, eight groups of shear tests were carried out to study the shear stiffness of inclined screws in timber–concrete composite beams with timber board interlayer. The key parameters included the embedment depth of the screw connector into timber, screw diameter, the thickness of concrete slab, and concrete strength. As indicated by the test results, the shear stiffness of the inclined screws was improved as the embedment depth of screw into timber and screw diameter increased. When the embedded depth of screw into concrete remained unchanged, the thickness of concrete slab and concrete strength exhibited no significant impact on the shear stiffness of inclined crossing screws. On the basis of the theory of a beam on a two-dimensional elastic foundation, the calculation method for predicting the shear stiffness of inclined screw in timber–concrete composite beams with interlayer was proposed. The comparisons demonstrated that the shear stiffness of inclined screw can be well predicted using the calculation method.

Parametric study to maximize the peak load shifting and thermal comfort in residential buildings located in cold climates

• Conducted a parametric study on an electrically heated floor operated by a self-learning control system. • Considered concrete/insulation thickness, floor/air limit temperature, and fan speed as the parameters. • Proposed a trade-off Taguchi-ANOVA approach for multi-objectives: peak shifting, thermal comfort and cost saving potential. • Among all the factors, insulation thickness was found to have the highest significance. In recent years, several peak load-shifting strategies were proposed to bridge the temporal mismatch between energy supply and demand in residential buildings. In cold climate regions (e.g., Quebec), most residential buildings are constructed with wood and are considered light-weight buildings. In such buildings, concrete slabs in the basement have the highest energy storage capacity, and hence, possibilities for peak load shifting (through energy storage) in all the floors of the building are limited. In this regard, a forced ventilation system or heat extraction system (HES) was proposed in the literature to transfer the hot air from the basement to other floors. Though the solution for peak load shifting in the entire house is available, still, the question on optimal conditions to enhance the peak load shifting potential as well as compromises on the thermal comfort and capital cost are left unanswered. Understanding these was the motivation of this study, and subsequently, a parametric study was carried out on the components involved in buried electrically heated floors (BEHFs) integrated with HES. Achieving higher peak shifting while guaranteeing occupants’ thermal comfort and lower capital cost were considered as the responses. For the parametric study, five factors namely concrete slab thickness, insulation thickness, fan speed as well as the upper limit for indoor air temperature and floor surface temperature were considered with three levels. The simulation results showed that for most of the cases, insulation thickness had the most significant effect among the factors. The main finding of this research is providing insights on overall optimal conditions for selecting the BEHF and fan parameters to achieve higher peak shifting potential and thermal comfort with a lesser capital cost. Since there are around 1.6 million detached houses in Quebec (with similar building characteristics considered in this study), the obtained optimal conditions can be used as a guideline for both supply and demand sides to achieve higher peak shifting, thermal comfort and heating cost savings.

Simple Empirical Temperature Gradient Prediction Model for Jointed Plain Concrete Pavements: Development and Validation

The aim of this paper is to propose a simple empirical prediction model for temperature gradients within concrete slabs of jointed plain concrete pavements (JPCPs) based on data collected by the Pavement Conditions Monitoring System at Shanghai Pudong International Airport. Temperature data (7,056 data sets) were obtained at the center and corner of the concrete slab and evaluated via statistical analysis. Equivalent linear temperature gradients were employed to quantify the nonlinear temperature profiles throughout the depth of the concrete slab. The surface temperature was obtained via the regressed quadratic function of the temperature profile. For simplicity and effectiveness, concrete slab thickness, surface temperature, air temperature, and time were selected as the input variables. A simple empirical model for predicting the temperature gradient in the concrete slab was developed using multiple regression analysis and validated by field temperature data. The results show no significant difference between the temperatures measured at the center and corner of the concrete slab. Hence, measurement location appears to have little effect on the monitoring of temperature in JPCPs. The results also show that the calculated surface temperature is valid for establishing the empirical model. Moreover, the statistical analysis results indicate that the empirical model fits the data well and all the coefficients in the model are significant at 5% significance. The final results of the model validation demonstrate that the proposed empirical model is reliable and can be conveniently used to predict the temperature gradients within concrete slabs of JPCPs.

Punching shear behavior of rubberized concrete slab

Punching shear of flat slabs made from normal concrete is a local, brittle failure that may occur before the ductile flexural failure. Since the concrete technology introduced alternative materials into concrete to promote the sustainability by using recycle material such as agriculture waste and industrial by product, the quality of this concrete need to be investigate further in all aspect. Therefore, this study is initiated to investigate the performance of concrete containing rubber to be used as structural element. This study is investigated the behavior of rubberized concrete flat slab subjected to the punching load. The effect of rubberized concrete and different slab thickness to the punching shear strength is main consideration in this investigation. The study is started by evaluating the mechanical properties of rubberized concrete such as compressive strength, flexural strength and splitting tensile strength. In comparison to normal concrete, the mechanical properties of rubberized concrete shown a reduction in compressive strength and increase in flexural strengths and split tensile strength. The performance of rubberized flat slab is observed in term of punching shear strength, critical perimeter and displacement by using experimental approach. Punching shear strength and development of crack within critical perimeter are observed during experimental test. Punching shear strength produced by experiment test is compared to values obtained by established equations from EC2 and ACI 813. From this comparison, it is indicated that the equations are over predicted the punching shear strength in the range of 12 – 72 %. Rubberized concrete slab exhibited ductile failure and underwent significant displacement before reaching punching fracture. Critical perimeter produced by rubberized concrete slab also extended more than produced in the normal concrete in the range of 34 - 75%. The punching shear strength of rubberized concrete slab also exhibited a significant reduction in punching shear resistance compared to normal concrete for the similar slab thickness. As conclusion, the rubberized concrete produced better critical perimeter at the lower punching shear resistance.

Cellular Automata Approach to Hydration Heat of Concrete Based on Equivalent Time

Cellular automata can be used to analyze a physical system which is satisfying differential equations. A cellular automata program for a thermal analysis of hydration heat was developed. Based on the fundamental theory of cellular automata, the heat conduction equation was deduced for validating the cellular automata approach. By introduction of the concept of equivalent time, the variation of the chemical reaction rate of hydration heat with temperature was studied by use of the Arrhenius function. The relationship between the adiabatic temperature rise and equivalent time was determined by analyzing testing data．A parametric analysis of ambient temperature and concrete slab thickness was also conducted. The temperature rise of concrete increases with increasing ambient temperature and thickness of the slab.