Slab Elements Research Articles

Experimental Testing of CFRP-Strengthened Reinforced Concrete Slab Elements Loaded by Close-In Blast

Strengthening reinforced concrete slab or wall structural elements with carbon fiber-reinforced polymer (CFRP) can improve their blast resistance. However, close-in blasts (blasts with a scaled range of less than 0.4 m/kg1/3) may undermine the effectiveness of the CFRP strengthening. This paper presents an experimental testing program on CFRP-strengthened reinforced concrete slab specimens that utilized fiber anchors. Two CFRP mitigation designs were tested under blast loads with a scaled range of 0.4 and 0.6 m/kg1/3. Tests on unmitigated reinforced concrete slab specimens provided baseline comparisons. The experimental results showed that the use of CFRP strengthening improved the blast resistance of reinforced concrete slab specimens. For a larger scaled range, 0.6 m/kg1/3, the CFRP successfully prevented flying debris and reduced the overall deflections of the slab specimens. However, for the closer scaled range, 0.4 m/kg1/3, the high shock blast pressures shattered the concrete through the thickness of the slab specimen and tore through the back-face CFRP. However, back-face velocity and overall deflections were reduced by about 75% compared to the baseline test slab specimen.

Ferrocement sandwich and hollow core panels for floor construction

This paper presents the results of a research work to develop ferrocement sandwich and hollow core panels for use as precast one way slab elements. Sandwich panels consisted of two thin ferrocement layers reinforced with steel wire mesh and a core of autoclaved aerated lightweight concrete bricks. The hollow core panels are made of the same ferrocement mortar matrix with three circular holes of 75 mm diameter running along the length of the specimen. A total of 15 sandwich panels and 12 hollow core panels were cast and tested under flexural loadings. The experimental results showed that high ultimate and service loads, crack resistance control, high ductility, and good energy absorption could be achieved by using the proposed panels. A theoretical model based on the ultimate strength method for reinforced concrete was developed to determine the ultimate moment and mode of failure of the panels. The theoretical and experimental results showed good agreement.

Analysis of Slab and Beam’s Moment Influenced by Stiffness Ratio

In this paper ,taking industrial factory building , the size of 33 * 19.8 m2 for example, analyzes Integral reinforced concrete floor system under the loads by Finite element analysis software ANSYS. In the calculation process, beam element is beam4, slab element is shell63, Changing the line stiffness ratio of beam and slab, main beam and secondary beam, researches of moment on the main beam and the secondary beam by means of line stiffness ratio. It is showed that , when the value of line stiffness ratio is more than 10, mid-span moment is fewer obviously with the Increasing K ; when the value of line stiffness ratio is between 2 and 5, mid-span moment is fewer, too; when the value of line stiffness ratio is shorter than 2, mid-span moment does almost not changed.

Application of GQJS in Calculation for Construction Process of Continuous Box Girder Bridge with Corrugated Steel Webs

AbstractIn order to study the deformation features of box girder with corrugated steel webs, based on the project of Juancheng Yellow River Highway Bridge, two element-modeling methods were adopted to perform the finite element analysis throughout the construction process by Highway Bridge Design Analysis Software (Chinese name abbreviation: GQJS). In the first method (One-node Method for short), elements of top and bottom concrete slabs as well as steel webs share the same nodes, agreeing with the assumption of plane section. And plain steel webs were adopted instead of corrugated steel webs. In order to take into account the accordion effect of corrugated webs, the reduction elastic modulus of Q345 steel was determined according to equivalent axial stiffness. In the second method (Two-node Method for short), nodes of elements of top and bottom concrete slabs were independent relatively and elements of corrugated steel webs connect with elements of top and bottom concrete slab. In this case, relative dis...

Steel-Concrete Composite Beams for Slim Floors–Specific Design Features in Scope of Steel Frames Design

Welded steel beams with trapezoidal box cross-sections and specially punched webs were developed to be preferably applied together with hollow core pre-stressed concrete slabs as composite beams in slim floors. Heights of standard produced Deltabeams copy the range of produced HC-units heights. Utilization of these slim composite beams enables to achieve an effective solution also in combination with filigree or in-situ cast concrete decks. Optimized solutions development from point of view of minimized structural height, high load carrying capacity, simply and very fast erection, versatile utilization and standardized details creates a solid basis for successful and technically efficient usage, not only in scope of concrete, but also steel and composite constructional systems. Reliable solution of fire resistance up to R180, proved by several realized fire tests and supported by appropriate design procedures, eliminates any needs for special on fire case oriented additional structural improvements. Design process in agreement with EC3 and EC4 covers with complexity all the relevant bearing capacity and structural stiffness questions for beams and also for supported slab elements. Specific requirements on acceptable parameters of floor vibrations are covered by experience and tests, carried out on realized structures and supported by suitable calculation models. All unique solutions are verified as a standard by corresponding experimental methods. Utilization of Deltabeams in slim floors is saving constructional heights, reduces energy consumption in buildings, simplifies the realization of constructional cable and pipe lines; parallel to that it significantly reduces time of erection and total costs. Paper presents specific requirements on slim floor Deltabeams in the field of ultimate and serviceability limit states and joint design suitable in steel frames. Requirements on floor vibration acceptance, methods and principles on how to achieve the project defined fire resistances are listed as well.

A Parametric Study of the Reinforced Concrete Slab Subjected to Dynamic Excitation

The width of effective slab to estimate the beam flexural strength at the beam ends in structures subjected to lateral loading, such as earthquake, is not explicitly addressed in design codes. As a result, designers often ignore the contribution of floor slabs to the lateral load resistance. There is a need for a simple model to assess the slab contribution to beam strength for analysis and design. General expressions for the yield loading and stiffness characteristic of the slab element have been developed which is more sensitively depend on yield line theory beside other parameters such as spacing, yield strength, area of reinforcement, and the span length. A model considering beam growth, bending effects and the slab effect is being considered in the present work. The results of the analytical investigation are compared with experimental results. The slab element model is then used to conduct a parametric study aiming to investigate the effect of the distribution and strength of the slab steel. It is shown that the performance of the unit is directly related to this steel.

정적 및 동적 해석을 통한 철근콘크리트 무량판 구조의 연쇄 붕괴 저항 성능 평가

현재 한국에서는 연쇄 붕괴에 대한 설계지침이 적용되고 있지 않으며, 특히 무량판 구조의 연쇄 붕괴 저항 성능에 대한 연구는 초기단계라고 할 수 있다. 따라서 이 연구에서는 철근콘크리트 무량판 구조의 연쇄 붕괴 저항 성능을 평가하기 위하여 3가지 해석법을 수행하였다. 선형 정적 해석을 통하여 GSA의 대체경로법에 의한 DCR 값의 차이를 비교하였고, 선형 동적 해석을 통하여 기둥 제거 이후의 수직 변위를 비교하였으며, 비선형 정적 해석을 통하여 최대 하중 계수를 판단하였다. 유효 보폭 모델과 판 유한 요소 해석 모델의 차이점을 분석하기 위하여 여러 변수들에 따라 유한 요소 해석이 수행되었다. 무량판 구조에서 실무에서 많이 사용되고 있는 유효 보폭으로 모델링하는 방법은 슬래브의 강성 기여도를 반영하고 있지 못해 연쇄 붕괴 성능 평가는 상세 유한 요소 해석이 적절할 것으로 판단된다.여러 변수들을 종합 모서리 기둥(CC)을 제거할 경우가 가장 불리한 조건이고, 내부 기둥(IC)이 제거될 경우가 가장 유리한 조건으로 나타났다. 이 연구에서 제시된 무량판 구조의 연쇄 붕괴 저항 성능 결과로부터 향후 무량판 구조의 성능을 합리적으로 평가하는데 유용하게 활용될 수 있을 것으로 사료된다.

Experimental and numerical studies on concrete encased embossments of steel strips under shear action for composite slabs with profiled steel decking

The subject of the ongoing research work is to analyze the composite action of the structural elements of composite slabs with profiled steel decking by experimental and numerical studies. The mechanical and frictional interlocks result in a complex behaviour and failure under horizontal shear action. This is why the design characteristics can be determined only by standardized experiments. The aim of the current research is to develop a computational method which can predict the behaviour of embossed mechanical bond under shear actions, in order to derive the design characteristics of composite slabs with profiled steel decking. In the first phase of the research a novel experimental analysis is completed on an individual concrete encased embossment of steel strip under shear action. The experimental behaviour modes and failure mechanisms are determined. In parallel with the tests a finite element model is developed to follow the ultimate behaviour of this type of embossment, assuming that the phenomenon is governed by the failure of the steel part. The model is verified and applied to analyse the effect of embossment's parameters on the behaviour. In the extended investigation different friction coefficients, plate thicknesses, heights and the size effects are studied. On the basis of the results the tendencies of the ultimate behaviour and resistance by the studied embossment's characteristics are concluded.

Finite Element Analysis of Vibrating Frequency for Skew Slab Bridge Based on Finite Strip Thought

Based on the finite strip thought and displacement interpolation function of Bernoulli-Euler beam element, using the transformation relationship between skew coordinate and Cartesian coordinate system, a new kind of thin parallel slab element was established, element stiffness matrix and consistent mass matrix were derived. The vibrating frequency of simply supported skewed slab was calculated. Computing results were compared with theoretical results and Ansys results. The maximum error was 2.68%. Changing the mesh density of skew slab, the convergence of present element was tested. Examples show that this element has the features of high precision and strong convergence. At last, the vibrating frequency coefficients of skew slab bridge with different ratios of span to width were provided, which can be adopted to compute the vehicle’s impact factor of skew slab bridge by specification method.

A design-oriented model for the collapse resistance of composite floors subjected to column loss

A design-oriented model is proposed for computing the load-resisting capacity of composite steel–concrete floors subjected to interior column loss. The model is based on the premise that floor collapse is resisted through the development of membrane action in the slab elements and catenary forces in the steel beams. A number of simplifying assumptions are made in the model pertaining to the deformed shape of the system, development of failure-resisting mechanisms, and overall system behavior. The proposed model is incremental in nature and tracks the evolution of damage in a floor system loaded up to failure. The model is shown to be able to capture the effect of influential variables on collapse resistance. Key limitations on the model are highlighted and discussed.

Experimental and analytical assessment of ductility in lightly reinforced concrete members

This paper is concerned with the ultimate behaviour of lightly reinforced concrete members under extreme loading conditions. Although the consideration given to the assessment of ductility is of general relevance to various applications, it is of particular importance to conditions resembling those occurring during severe building fires. The main purpose of the investigation is to examine the failure of idealised members representing isolated strips within composite floor slabs which become lightly reinforced in a simulated fire situation due to the early loss of the steel deck. An experimental study, focusing on the failure state associated with rupture of the reinforcement in idealised concrete members, is presented. The tests enable direct assessment of the influence of a number of important parameters such as the reinforcement type, properties and ratio on the ultimate response. The results of several tests also facilitate a detailed examination of the distribution of bond stresses along the length. After describing the experimental arrangements and discussing the main test results, the paper introduces a simplified analytical model that can be used to represent the member response up to failure. The model is validated and calibrated through comparisons against the test results as well as more detailed nonlinear finite element simulations. The results and observations from this investigation offer an insight into the key factors that govern the ultimate behaviour. More importantly, the analytical model permits the development of simple expressions which capture the influence of salient parameters such as bond characteristics and reinforcement properties, for predicting the ductility of this type of member. With due consideration of the findings from other complementary experimental and analytical studies on full slab elements under ambient and elevated temperatures, this work represents a proposed basis for developing quantified failure criteria.

Modelling of reinforced concrete structures in fire

In this paper a robust finite-element procedure is presented for three-dimensional modelling of reinforced concrete structures under fire conditions. In this non-linear procedure a reinforced concrete building is modelled as an assembly of finite plain beam–column and slab elements, reinforcing steel bar elements and bond-link elements. Both material and geometric non-linearities are considered in the model. To consider the effects of concrete spalling on the thermal and structural behaviours of concrete structures under fire conditions, a ‘void layer' and ‘void segment' are introduced to represent the spalled-concrete part within concrete slabs, beams and columns. A critical temperature is used as the concrete spalling criterion. These developments enable the model to simulate quantitatively the effects of concrete spalling on both the thermal and structural behaviours of reinforced concrete structures in fire. A series of analyses are also conducted on a generic reinforced concrete building. The results indicate that, under fire conditions, the structural behaviour of isolated members with the concrete spalled is very different compared with the behaviour exhibited when embedded within a building. The influence of bond conditions between concrete and reinforcing steel bars on the fire resistance of structural members is significant. The global structural fire resistance of the reinforced concrete building is significantly affected by the concrete spalling on their members, in which the most important member is floor slabs.

A new shear-flexible FRP-reinforced concrete slab element

In this paper, a simple shear-flexible rectangular layered FRP-reinforced concrete slab element is developed based on Mindlin–Reissner plate theory and Timoshenko’s composite beam functions for nonlinear finite element analysis of FRP-reinforced concrete slabs. The Timoshenko’s composite beam functions are developed for FRP-reinforced concrete slabs based on those for composite laminates. The plane displacement interpolation functions of a quadrilateral isoparametric element with drilling degrees of freedom are employed to describe the membrane effects and the bending effects of the slab element are represented by the rotation functions of the slab element derived from Timoshenko’s composite beam functions. Both geometric nonlinearity and material nonlinearity of the materials are included in the new element. The efficiency of the element for nonlinear finite element analysis of FRP-reinforced concrete slabs is validated by comparing the computed results of two numerical examples with those obtained from lab tests.

Ultimate Behavior of Idealized Composite Floor Elements at Ambient and Elevated Temperature

This paper is concerned with the ultimate behavior of composite floor slabs under extreme loading situations resembling those occurring during severe building fires. The study focuses on the failure state associated with rupture of the reinforcement in idealized slab elements, which become lightly reinforced in a fire situation due to the early loss of the steel deck. The paper describes a fundamental approach for assessing the failure limit associated with reinforcement fracture in lightly reinforced beams, representing idealized slab strips. A description of the ambient-temperature tests on isolated restrained elements, carried out to assess the influence of key material parameters on the failure conditions, is firstly presented. The results of a series of material tests, undertaken mainly to examine the effect of elevated temperature on ductility, are also described. A simplified analytical model is employed, in conjunction with the experimental findings, to assess the salient material parameters and their implications on the ultimate response at both ambient and elevated temperature.

Modeling of mechanical response of FRP composites in fire

A thermomechanical model is presented for predicting the time-dependent deflections of cellular FRP slab elements subjected to mechanical loading and fire from one side. The model comprises temperature-dependent mechanical property sub-models for the Young’s modulus, viscosity and coefficient of thermal expansion. Two different thermal boundary conditions were investigated: with and without liquid-cooling of the slab elements in the cells. A finite difference method was used to calculate the deflection at each time step. Deflections resulting from stiffness degradation due to glass transition and decomposition of the resin dominated over those resulting from viscosity and thermal expansion. The predicted total deflections compared well with the measured results over a test period of up to 2 h. The failure mode of the non-cooled specimen could be explained.

Pre-cast Concrete Slab/Column Joints: Experiments and Design Models

The applications of pre-cast concrete in flat-slabs are mainly controlled by the construction joint between the slab elements and columns in order to satisfy monolithic action. This paper introduces a conceptual approach for the construction detail of such joints. An experimental program was conducted for testing the joints between two pre-cast cantilever slabs and a rectangular column. At the cast-in-situ joints, the slabs’ and columns’ loop reinforcement were arranged in a staggered overlapped manner. The tested specimens were loaded asymmetrically under bending, in order to study the moment transfer efficiency and the rotational stiffness of the joint from zero load up to failure. Several variables were studied; the slab reinforcement ratio and distribution, the curvature shape of the column loop reinforcement and the arrangement of shear studs. The behaviour of those construction joints was compared to that of ordinary monolithic flat slab/column joint to evaluate cracking and deformational behaviour at service as well as their ultimate capacities. Additionally, the structural behaviour of those joints was discussed using Strut and Tie Method (STM). Design Models using STM are introduced, which can be adopted in the design of such joints.

The effect of 3D and 2D deformations on flattened wires

To investigate the effect of 3D and 2D deformations on flattened wires, the effective strain fields of flat rolled and sidepressed wires are predicted using the combined finite and slab element method (FSEM) and two-dimensional finite element method (TDFEM), respectively. The validity of the calculated strain fields are verified using the Vickers microhardness test. Utilizing the calculated strain fields, the strain inhomogeneity of the flat rolled and sidepressed wires are investigated. To assess the effects of height to width ratio and frictional condition on the strain inhomogeneity, an inhomogeneity factor (IF) is defined. The results show that for both the flat rolled and sidepressed wires the strain inhomogeneity is increased with increasing the height to width ratio and friction factor. Moreover, for a specific height to width ratio and frictional condition, the strain inhomogeneity of flat rolled wire is lower than that of sidepressed wire.

Analysis of the pump-beam path in corner-pumped slab laser

The propagation of the pump radiation in active slab elements is considered. Conditions of the total internal reflection of the pump radiation are obtained, and are used to construct a series of graphical illustrations of reflection characteristics of different active elements.

Nonlinear analysis of orthotropic composite slabs in fire

In this study an orthotropic slab finite element is developed to model orthotropic slabs in fire, using a layered 9-noded isoparametric slab element and a 3-noded beam element. The element is assembled from a solid slab element which represents the continuous upper portion of the profile, and a special beam element which represents the ribbed lower portion. An equivalent width for the cross-section of this beam element is determined according to the dimensions of the solid slab element and the cross-section of the ribbed profile, and the beam shares the nodes of the solid slab element. The temperature within each layer of the slab element can vary between adjacent Gauss integration points so as to reflect temperature variations in the horizontal plane. Several fire tests on composite slabs have been modelled to validate the approach. Cases of orthotropic slabs with wide range of parameters defining the ribbed profile have been studied, which show that the orthotropic slab model is robust and effective in reflecting the influence of the shape of ribs on the thermal and structural performance of the slabs in fire. The study shows the influence of decking shape on the thermal and structural behaviours of orthotropic slabs. A simple evaluation method for profile selection is proposed.

NUMERICAL MODEL OF THREE‐DIMENSIONAL COUPLED WALL STRUCTURES

Three‐dimensional description of a building structure taking into consideration the soil structure interaction is a very complex problem; the solution of it is often obtained by the finite‐element method. However, this method takes a significant amount of computational time and memory. Therefore an efficient computational model based on the subdivision of the structure into building elements such as wall and floor slab elements, plane and three‐dimensional joints and lintels, that could provide accurate results with a significantly reduced computational time, is proposed in this study for the analysis of three‐dimensional structures. The examples prove the efficiency and the computing possibilities of the model.