Structural behavior and m–k value of composite slab utilizing concrete containing crumb rubber

Many research works have been conducted to study the fresh and hardened properties of concrete containing crumb rubber as replacement to fine aggregate. The outcome of these researches indicated that though the compressive and flexural strength of crumb rubber concrete (CRC) decreased as percentage of fine aggregate replacement increased; the CRC has lower unit weight, better slump values, better toughness and absorb more energy before failure. In view of the fact that the main strength of composite floor slab lies within the bond between the concrete and the profiled steel sheeting, therefore the using of more ductile concrete such as CRC to toping the profiled steel sheeting could produce a new composite slab system. Two sets of slabs; each set comprising three CRC composite slabs and one conventional concrete slab has been tested with two shear span (450 and 900 mm). The results showed that the CRC slabs behavior could be characterized as ductile, while the m–k value has been found to be 80.7 and 0.037, respectively.     

Static tests on a soil–steel bridge structure with a relieving slab

The paper deals with a new, arch road bridge made from structural corrugated plates, over the Plawna Stream, on a local road between Bystrzyca Klodzka and Ladek Zdroj in Stary Waliszow, Poland. The bridge replaced the old stone arch bridge that was destroyed during the flood of 1997. The steel bridge is founded on two continuous footings made of reinforced concrete. Its effective span is 10.00 m and its clear height is 4.02 m. The results of tests carried out on the bridge under three static load schemes after four years of service are presented. The average values of the measured displacements and strains in selected points and elements of the steel shell structure were found to be considerably lower than the ones calculated for the same load. Since designs of this type are more and more often adopted for small- and medium-size bridges, the conclusions drawn from the presented tests can be generalised to the whole class of such bridge structures.     

Experimental and theoretical studies on composite steel–concrete box beams with external tendons

Composite steel–concrete box beams with and without external tendons were tested to their ultimate strength. The effects of external tendons on structural performance of composite steel–concrete beams were investigated in detail. Experimental results proved that, due to the action of external prestressing tendons, the ultimate strength of a composite steel–concrete box beam increased by 27.72%, the elastic limit of a composite steel–concrete box beam increased by 29.17%, the stiffness of a composite steel–concrete box beam increased by 54.15% at the failure state, and the deflection ductility of a composite steel–concrete box beam increased by 18.00%. The equation for estimating the stress in external prestressing tendons is established according to the relationship between the stress in external tendons, and the maximum compressive strain of concrete slab. Based on experimental results, a theoretical model for predicting the flexural resistance of composite steel–concrete box beam with external tendons is proposed. The spatial integral method, which adopts the actual stress distribution, is more rational than the conventional equilibrium rectangular stress block model, and is adopted to calculate the interior force on sections. The calculated flexural resistance based on proposed equations has a high level of accuracy, when compared with test results. Experimental and theoretical studies have demonstrated that the composite steel–concrete box beam with external tendons is a promising innovative structure that combines the merits of composite steel–concrete box beams and external prestressing tendons.     

Numerical investigation of inelastic buckling of steel–concrete composite beams prestressed with external tendons

The ultimate resistance of a continuous composite beam is governed by either distortional lateral buckling or local buckling, or an interactive mode of the two which is sharply different from the torsional buckling mode in a bare steel beam. A finite element model is developed and based on the proposed FE model, inelastic finite element analysis of composite beams in negative bending is investigated, considering the initial geometric imperfection and the residual stress patterns and the FE results are found agree well with the test results. Parametrical analysis is carried out on the prestressed composite beams with external tendons in negative bending. Factors that influence load carrying performance and buckling moment resistance of prestressed composite beams are analyzed, such as initial geometric imperfection, residual stress in steel beams, force ratio, which is defined as the extent of prestressing force and negative reinforcement in the beams, as well as the slenderness ratios of web, flange, and beams. By varying cross-section parameters, 25 groups of composite beams under negative uniform bending with initial geometric imperfection, residual stress as well as different force ratios, 200 beams in total are studied by means of the FE method. The computed buckling moment ratios are drawn against the modified slenderness proposed by the authors and compared with the Chinese Codified steel column design curve. It is demonstrated that the tentative design method based on the Chinese Codified design curve can be used in assessment of buckling strength of composite beams in a term of the modified slenderness defined.     

Structural fire performance of earthquake-resistant composite steel–concrete frames

Seismic and fire design of a building structure may be two very demanding tasks, especially if included in a performance based design philosophy. For the time being, the necessary harmonization on the regulations concerning these two design fields is almost missing, thus preventing the effective possibility of an integrated design. Besides, while many countries have already moved towards the use of performance-based codes for seismic design, the application of such methodologies for the fire design of structures is still limited in scope. Within this framework, the development of suitable procedures introducing structural fire performance issues for a comprehensive design methodology is needed.In this paper, a numerical investigation for the assessment of the structural fire performance of earthquake resistant composite steel–concrete frames is presented. With reference to a case study defined in the framework of a European Research Project, a great effort was devoted to the identification of the key structural parameters allowing for a possible correlation between the predictable performances under seismic and fire loadings, when these two are considered as independent actions.At the conceptual design level, the most suitable structural solution with respect to both design actions was chosen, including composite beams and circular steel concrete-filled columns. The frame was designed in order to resist severe seismic action according to the ductile design approach provided by Eurocode 8; the parameters affecting members’ sizing were outlined in this phase. Afterwards, the seismic performance of the designed frame was investigated by means of non-linear static analyses; once the seismic performance objectives were met, in order to evaluate the structural fire performance of the whole frame a set of criteria was defined. To this purpose, thermo-mechanical analyses under different boundary conditions were developed and in order to identify the possible mechanisms leading to structural failure, the state of stress at the critical cross-sections at different times of fire exposure was investigated. Another point of main concern was represented by the assessment of the influence of different restraining conditions on the achieved fire resistance rating and kind of structural failure.Moreover, the proposed methodology allowed making an estimate of the amount of axial restraint provided to the heated beams by the surrounding structure; in this view, the importance of choosing column elements in function of their flexural stiffness was revealed, in order to correlate it with the predictable performances under both seismic and fire loadings.     

Impact tests on steel–concrete–steel sandwich beams with lightweight concrete core

This paper studies the impact performance of Steel–Concrete–Steel (SCS) sandwich beams consisting of a lightweight concrete core sandwiched between two face plates that are connected by J-hook connectors. Impact tests were carried out by dropping free weights on to sandwich beams to investigate their structural response against impact loads. Test results revealed that the proposed J-hook connectors provide an effective means to interlock the top and bottom steel face plates, preventing them from separation during impact. The use of fibres in concrete core and J-hook connectors for composite action enhances the overall structural integrity of the sandwich beams when compared with those without such enhancement. An elastic–plastic analysis method is developed to predict the force-indentation relationship of sandwich sections subjected to local impact. Dynamic analysis based on the local force-indentation relationship is carried out to predict the impact force and global response behavior of the sandwich beams. The predicted results are compared with those obtained from the tests to validate their accuracy so that they can be used to evaluate the performance of sandwich beams under low velocity hard impact.     

Modeling the response of composite beam–slab assemblies exposed to fire

This paper presents the development of a three-dimensional nonlinear finite element model for evaluating the response of composite beam–slab assemblies subjected to a combination of gravity and fire loading. The behavior of typical beam–slab assemblies with different shear connection types (welded–bolted shear tab and all-bolted double-angle connection), exposed to different fire scenarios, was modeled using ANSYS. The finite element model accounts for temperature dependent thermal and mechanical properties of constituent materials, connections, and composite action. Transient time domain coupled thermal-stress analysis is performed to obtain the temperature distribution and deformation response of the composite beam–slab assembly. The finite element model is validated by comparing the predicted and measured thermal and structural response parameters of three composite beam–slab assemblies tested under fire conditions. The comparisons show that the proposed model is capable of predicting the fire response of beam–slab assemblies with good accuracy. Research from the analysis clearly shows that the composite action between the beam and slab significantly enhances the fire performance of composite beam–slab assemblies. It is concluded that the proposed finite element model could be used as a feasible tool to evaluate the fire response of composite floor systems.     

Lightweight steel–concrete–steel sandwich system with J-hook connectors

This paper investigates a new concept for designing composite structures comprising a lightweight concrete core sandwiched in between two steel plates which are interconnected by J-hook connectors. Specifically, lightweight concrete (density less than 1450 kg/m³) and novel J-hook connectors have been developed for this purpose. The hook connectors are capable of resisting tension and shear, and their uses are not restricted by the core thickness. Push-out tests confirms that the shear transfer capability of J-hook connector is superior to the conventional headed stud connector in achieving composite action between steel plate and concrete core. Twelve sandwich beam specimens have been tested to evaluate the flexural and shear performance subjected to static point load. Parameters investigated include degree of partial composite, concrete with and without fibres and concrete strength. Using Eurocodes as a basis of design, theoretical model is developed to predict the flexural and shear capacity considering partial composite and enable construction of sandwich structures with J-hook connectors. Compared with test results, the predicted capacity is generally conservative if brittle failure of connectors can be avoided. Test evidence also shows that inclusion of 1% volume fraction of fibres in the concrete core significantly increases the beam flexural capacity as well as its post-peak ductility.     

Ultimate load behaviour of webs in steel–concrete composite plate girders

The paper is concerned with the tension field action in webs of steel–concrete composite plate girders. A three-dimensional finite element model has been used to carry out nonlinear analyses on composite plate girders. The results obtained from the finite element analyses are compared with those from experiments. It is observed from the comparative study that the proposed nonlinear finite element model is capable of predicting the ultimate load behaviour of steel–concrete composite plate girders to an acceptable accuracy. Results are presented to explain the development of the tension field action in the webs and to illustrate a measure of the contribution by the concrete slab acting compositely with the girder to the changes in tension field compared to a plain steel girder.     

Dynamical identification and modelling of steel–concrete composite high-speed railway bridges

In the last few years, the construction of new high-speed (HS) railways across Europe, as well as in many other countries, has required many different bridges and viaducts. Together with classical concrete solutions, new steel–concrete composite typologies have been developed, giving light and cheap structures. Despite these studies and applications, some concerns still remain about the definition of reliable models for the evaluation of their actual dynamical behaviour under HS train passage. In particular, the influence of many structural and non-structural components, such as cross-girders and ballast, are still not well recognised. In this paper, open problems related to the dynamical assessment and modelling of new steel–concrete four-parallel-girder and box-girder solutions are exposed and analysed. A suitable procedure, based on operational modal analysis, model updating and train–bridge interaction analysis is applied to two bridges, recently built in the new Italian HS network, in order to assess and verify their dynamic behaviour under operative conditions.     

An isogeometric approach for the analysis of composite steel–concrete beams

An isogeometric approach based on non-uniform rational B-spline (NURBS) basis functions is presented for the analysis of composite steel–concrete beams. A refined high-order theory is considered in deriving the governing equations using the principle of virtual work. The employed theory satisfies all the kinematic and stress continuity conditions at the layer interfaces and considers effects of the transverse normal stress and transverse flexibility. The global displacement components, described by polynomial or combinations of polynomial and exponential expressions, are superposed on local ones chosen based on the layerwise concepts. The present isogeometric formulation does not need incorporating any shear correction factor. Moreover, in the present isogeometric formulation, the number of unknowns is independent of the number of layers. The proposed isogeometric formulation is validated by comparing the present results with the available published and the three-dimensional (3D) finite element results. In addition to correctly predicting the distribution of all stress components of the composite steel–concrete beams, the proposed formulation is computationally very economic.     

Influence of test specimen on experimental characterization of timber–concrete composite joints

Load-carrying capacity of timber–concrete composite joints is usually evaluated using shear tests, which still lack specific standards. Regulations EN 26891 [1] and ASTM D 5652 [2] are usually used, both for timber joints, or EUROCODE 4 [3] for steel–concrete composite joints. Questions about test execution and arrangement of specimens are frequent and recurrent [4], [5], [6]. Steel–concrete composite structures already have a standard shear test for joints (push-out), described in Johnson and Anderson [7]. These authors also discussed the many differences in the results of shear tests because of differences in test methods before EUROCODE 4 [3] standardization.This paper presents some questions about the arrangement of test specimens for shear tests in timber–concrete joints. An experimental program was performed for this reason. The aim of the work was to compare shear test results using two different series of specimens most utilized in a review of the literature: the push-out type with concrete center and timber sides and the push-out type with timber center and concrete sides. 8.0, 10.0 and 12.5 mm diameter corrugated bars were used as connectors. Eucalyptus grandis Brazilian hardwood timber glulam was used. Two-component epoxy adhesive was used to glue the connectors into the timber. Average cylinder compressive strength of the concrete was 25 MPa (28 days old). Reinforcement was 6.0 mm diameter 500 MPa-yield-stress corrugated bars.The results showed that test specimen arrangement influenced the strength and deformation characteristics of timber–concrete composite joints. The specimen with the best shear strength was the concrete–wood–concrete type, similar to those used in steel–concrete composite structures. Since the arrangement of test specimen is an important factor in joint tests, it is recommended that further efforts be made towards standardization.     

Fatigue tests on straight steel–concrete composite beams subjected to hogging moment

This paper describes the fatigue behavior of composite steel and concrete beams subjected to negative bending moment. Fatigue tests with repeated load limited to initial cracking and stabilized cracking, were performed on two steel–concrete composite beam substructures respectively. Test results indicated that when the repeated load was equivalent to the initial cracking load, the fatigue test had only limited influence on beam stiffness or crack patterns. However, when the repeated load was equivalent to the stabilized cracking load, a number of residual cracks occurred in the initial static test and the beam became less stiff as the load cycles increase. Failure of the bond between studs and surrounding concrete was confirmed in intermediate static tests; flexural stiffness of studs became smaller as the increase of load cycles. In addition, final static tests were performed on fatigue test specimens and another specimen without fatigue test. The comparison indicated that when the repeated load was larger than the initial cracking load, fatigue test could decrease beam stiffness and its ultimate load carrying capacity.     

Flexural behavior of strengthened steel–concrete composite beams by various plating methods

The effect of pre-intermediate separation on the flexural behavior of strengthened steel–concrete composite beams by either adhesively bonded carbon fiber reinforced polymers (CFRP) sheet or welded/bonded steel plate was studied. In the case of strengthened by CFRP sheet, two different attachment patterns, namely, CFRP sheet wrapped around the flange of the I-beam and CFRP sheet wrapped around the flange along with a part of the web, were examined by testing four different strengthened steel–concrete composite beams under four point bending (4PB). Two of these beams were strengthened by fully bonded CFRP sheet with the two different patterns, while, the others are similar but have pre-intermediate debonding area of 50 mm length × flange width at the bottom surface of the lower flange. In the case of strengthened by steel plate, three different attachment patterns of steel plate to the soffit of the beams, namely, discontinuously welded, end welded, and bonded/welded steel plates, were also tested under 4PB.The experimental results showed that, there is no growth of the intermediate debonding before the yield of the lower flange occurred for all strengthened beams by CFRP sheet. After yielding, the beams with pre-debonding area showed lower flexural capacity than those with fully bonding due to the rapid growth of the intermediate debonding. On the other hand, there is a difference in the yield load between the three different patterns of the welded steel plates with a marginal difference in the elastic stiffness.     

A new type of steel–concrete composite channel girder and its preliminary experimental study

A new type of steel–concrete composite beam that is specifically applicable to railway bridges is presented. The beam is featured with a channel shaped section. For such a section, the U-section steel beam is prefabricated with steel plates and the interior side of the channel is cast with concrete. The steel plates and concrete are integrated through shear stud connectors and work together to distribute loads. This type of structure not only inherits the characteristics of traditional concrete channel beams but also possesses its own unique attributes, such as advantageous mechanical performances, facilitating construction process, and low maintenance cost etc. To develop a design method for this new type of structures, and based on some FEM analysis, a static test of four-point symmetric bending was designed on a simply supported steel–concrete composite channel beam model with 1/3 sectional scale and 1/4 length scale. Preliminary research was conducted on its bending capacity, stiffness, stress distribution, crack diagram etc. Experimental results revealed that the steel plates and the concrete slab integrated through shear stud connectors can work well together and the channel beam model presented a bending failure mode. The flexural load carrying capacities and deformations of the composite channel beam were also analyzed by the Section analysis method, and the results agreed well with those from the test.     

Development of a baseline for structural health monitoring for a curved post-tensioned concrete box–girder bridge

The establishment of a baseline is essential for long-term structural health monitoring and performance evaluation. Usually, field testing data and finite element (FE) model are two critical tools used to develop the baseline. In this paper, the establishment of the baseline field database for a curved post-tensioned concrete bridge with expansion bearings is first introduced to include the effect of varying temperature conditions on the field testing data. This database uses data collected from a full year and is based on an undamaged status. The development of a baseline FE model for the bridge is then discussed. Model updating for the FE model are detailed in this paper which includes calibration of material properties, utilization of spring bearing elements, and replacement of Mindlin plate elements (MP4) on box–girder by recently developed cracked Mindlin plate elements (MP4C) to represent the bridge service conditions. A good agreement in modal results has been observed between the baseline FE model and the baseline field data. The proposed structural health baseline can be used for near real-time damage detection, development of monitoring techniques, and condition assessment. Finally, as an application of the baseline, this FE model is used for an earthquake simulation with a selected ground motion on the bridge. The seismic analysis demonstrates the beneficial effect of the guided expansion bearings on the bridge deck in the longitudinal direction.     

A multidisciplinary approach for fatigue assessment of a steel–concrete high-speed railway bridge on Sesia river

Steel–concrete composite bridge solutions have been more and more exploited in the new high-speed (HS) lines of European railway networks. New design solutions, introduced during a period of quick expansion for railway networks, amplified open problems related to dynamic effects, train–bridge interaction phenomena, fatigue loadings, structural modelling, fatigue life and comfort. In this article, results obtained by long-term dynamic monitoring of Sesia viaduct, a medium span double-box composite bridge of the new Italian HS network, are described and analysed. Structural modal properties were determined in order to evaluate the real-time dynamic behaviour and its correlation with environmental conditions. A suitable numerical procedure was then implemented in order to identify typology, length and velocity of trains crossing the bridge, to evaluate the intensity of deck vertical accelerations as a function of train speed and to obtain a reliable evaluation of real traffic spectra. A final fatigue assessment on welded connections was executed evaluating fatigue spectra by the aforementioned real traffic spectra and assuming S–N curves obtained by suitably executed experimental tests.     

A beam finite element including shear lag effect for the time-dependent analysis of steel–concrete composite decks

The paper presents a beam finite element for the long-term analysis of steel–concrete composite decks taking into account the shear lag in the slab and the partial shear interaction at the slab–girder interface. Using the displacement approach, beam kinematics is developed from the Newmark model for composite beams with partial shear connection; warping of the slab cross section is caught with the product of an established function which describes the warping shape, and an intensity function that measures the warping magnitude along the beam axis. Time-dependent behaviour is considered through an integral-type viscoelastic creep law for the concrete. The numerical solution is obtained by means of the finite element method and a step-by-step procedure for evolution in time. A refined, locking free, 13-dof beam finite element is derived considering second and third order hermitian polynomials in order to ensure consistent interpolation of the displacements. The convergence test results and comparisons with the experimental results of composite beams subjected to sustained loads demonstrate the precision of the proposed method. Further applications to realistic cases show the accuracy of the proposed element and its ability to describe the elastic and the time-dependent behaviour of bridge composite decks.