Experimental study of hybrid composite beams

In this study, a new type of hybrid confining device, a perforated steel tube that is externally protected by a thin fiber reinforced polymer skin is proposed and experimentally investigated. Hybrid composite beams were fabricated by filling fresh concrete into the hybrid composite tube. Fifteen scaled-down square beams, which had varying numbers of perforated steel faces or ‘steel grids’ and a dimension of length 55.9 cm, height 10.1 cm, and width 10.1 cm, were prepared. Four-point bending tests were conducted on all the specimens. In addition to the load–displacement curves obtained from the tests, strain gages were installed to monitor the local strain distributions. Test results show that the grid tube encased specimens lead to higher specific strength and ductility than the solid steel tube encased counterparts. Compared to other configurations, the specific strength and ductility are the highest when all the four faces are made of steel grids.     

Effects of steel fiber addition on mechanical properties of concrete and RC beams

C20 and C30 classes of concrete are produced each with addition of Dramix RC-80/0.60-BN type of steel fibers (SFs) at dosages of 0, 30, 60 kg/m³, and their compressive strengths, split tensile strength, moduli of elasticity and toughnesses are measured. Nine reinforced concrete (RC) beams of 300 × 300 × 2000 mm outer dimensions, designed as tension failure and all having the same steel reinforcement, having SFs at dosages of 0, 30, 60 kg/m³ with C20 class concrete, and nine other RC beams of the same peculiarities with C30 class concrete again designed as tension failure and all having the same reinforcement are produced and tested under simple bending. The load versus mid-span deflection relationships of all these RC and steel-fiber-added RC (SFARC) beams under simple bending are recorded. First, the mechanical properties of C20 and C30 classes of concrete with no SFs and with SFs at dosages of 30 and 60 kg/m³ are determined in a comparative way. The flexural behaviours and toughnesses of RC and SFARC beams for C20 and C30 classes of concrete are also determined in a comparative way. The experimentally determined (mid-section load)–(SFs dosage) and (toughness)–(SFs dosage) relationships are given to reveal the quantitative effects of concrete class and SFs dosage on these crucial properties.     

Behaviour of eccentric loading of FRP confined fibre steel reinforced concrete columns

This paper presents results of testing 16 specimens, 12 of which as columns under different eccentricities and four as beams under four point loading regime. All 16 specimens were circular in cross section and were made of reinforced concrete. Four specimens served as reference specimens and were just made of reinforced concrete. The next four specimens were wrapped with carbon fibre reinforced polymers (CFRP). The next four specimens had steel fibres added to the concrete. The final four specimens were reinforced with steel fibres and wrapped with CFRP. From each group of specimens, one specimen was tested as a column under a concentric load, the second specimen was tested as a column under 25 mm eccentricity, the third specimen was tested as a column under 50 mm eccentricity, and the final specimen was tested as a beam under four point loading regime. The experimental programme proved that the introduction of fibres as well as wrapping the specimens with FRP improve the properties of concrete, especially its ductility.     

Testing of full-scale concrete bridge deck slabs reinforced with fiber-reinforced polymer (FRP) bars

This paper presents an experimental study investigating the behavior of FRP-reinforced concrete bridge deck slabs under concentrated loads. A total of eight full-scale deck slabs measuring 3000-mm long by 2500-mm wide were constructed. The test parameters were: (i) slab thickness (200, 175 and 150 mm); (ii) concrete compressive strength (35–65 MPa); (iii) bottom transverse reinforcement ratio (1.2–0.35%); and (iv) type of reinforcement (GFRP, CFRP, and steel). The slabs were supported on two parallel steel girders and were tested up to failure under monotonic single concentrated load acting on the center of each slab over a contact area of 600 × 250 mm to simulate the footprint of sustained truck wheel load (87.5 kN CL-625 truck). All deck slabs failed in punching shear. The punching capacity of the tested deck slabs ranged from 1.74 to 3.52 times the factored load (P_f) specified by the Canadian Highway Bridge Design Code (CHBDC) CAN/CSA S6-06. Besides, the ACI 440.1R-06 punching strength equation greatly underestimated the capacity of the tested slabs with an average experimental-to-predicted punching capacity ratio (V_exp/V_pred) of 3.17.     

Shear behavior of continuous reinforced concrete T-beams using wire rope as internal shear reinforcement

The use of wire ropes with high-strength and high flexibility as internal shear reinforcement can solve the difficulties encountered in bending higher strength steel bar and can provide a better shear behavior to concrete beams. Three two-span reinforced concrete T-beams were tested to failure in order to examine the possibility of the practical application of wire ropes as shear reinforcement. The measured shear capacities of beams were compared with predictions obtained from equations specified in ACI 318-08 and the mechanism analysis based on the upper-bound theorem of concrete plasticity. Test results showed that using spiral-type wire rope as shear reinforcement is highly favourable for controlling the diagonal crack width and enhancing the ductility of beams failing in shear. In particular, the high-strength of the wire ropes significantly promoted the shear capacity of concrete beams. When a limit stress of 420 MPa for wire ropes is employed, ACI 318-08 is highly conservative in beams with spiral-type wire ropes compared with the control beams with closed stirrups. In addition, ACI 318-08 is still conservative when using the equivalent yield strength of wire ropes. On the other hand, the predictions obtained from the mechanism analysis are in good agreement with test results, regardless of the type of shear reinforcement.     

Creep of concrete masonry walls strengthened with FRP composites

The objective of the research was to examine the creep behavior of masonry walls strengthened with FRP composites compared to that of conventional reinforcement. Eight full-scale (40 in wide by 96 in tall [1.02 m × 2.44 m]) unreinforced concrete masonry walls were constructed for testing long-term deflections out-of-plane. The walls were strengthened with externally bonded CFRP or GFRP composites. Two additional walls were constructed with mild steel reinforcement grouted in the center cell of the specimens. Long-term deflections due to creep in FRP reinforced walls were shown to be ≈22–56% higher than those of steel reinforced walls.     

Preliminary experimental investigation of the fatigue bond behavior of CFRP confined RC beams

This paper presents the results of the first phase of a study on the effect of the confinement provided by transverse carbon fiber reinforced polymer (CFRP) sheets on the fatigue bond strength of steel reinforcing bars in concrete beams. Reinforced concrete bond-beams 150 × 250 × 2000 mm were tested. The variables examined were the area of the CFRP sheets (none or one U-wrap CFRP sheet), the reinforcing bar diameter (20 or 25 mm) and the load range applied to the specimens. The results showed that increasing the bar diameter increased the fatigue bond strength for the unwrapped beams. The CFRP sheets increased the bond strength of the bond-beams with 20 mm bars. However, for the beams with 25 mm steel bars the failure mode changed from a bond splitting failure for the unwrapped beams to a diagonal shear failure for the CFRP wrapped beams, and there was little increase in fatigue strength. Finally, the bond failure mechanism for repeated loading is described.     

Experimental and finite element analysis on the steel fiber-reinforced concrete (SFRC) beams ultimate behavior

Steel fiber-added reinforced concrete (SFRC) applications have become widespread in areas such as higher upper layers, tunnel shells, concrete sewer pipes, and slabs of large industrial buildings. Usage of SFRC in load-carrying members of buildings having conventional reinforced concrete (RC) frames is also gaining popularity recently because of its positive contribution to both energy absorption capacity and concrete strength.This paper presents experimental and finite element analysis of three SFRC beams. For this purpose, three SFRC beams with 250 × 350 × 2000 mm dimensions are produced using a concrete class of C20 with 30 kg/m³ dosage of steel fibers and steel class S420 with shear stirrups. SFRC beams are subjected to bending by a four-point loading setup in certified beam-loading frame, exactly after having been moist-cured for 28 days. The tests are with control of loads. The beams are loaded until they are broken and the loadings are stopped when the tensile steel bars are broken into two pieces. Applied loads and mid-section deflections are carefully recorded at every 5 kN load increment from the beginning till the ultimate failure.One of the SFRC beams modeled by using nonlinear material properties adopted from experimental study is analyzed till the ultimate failure cracks by ANSYS. Eight-noded solid brick elements are used to model the concrete. Internal reinforcement is modeled by using 3D spar elements. A quarter of the full beam is taken into account in the modeling process.The results obtained from the finite element and experimental analyses are compared to each other. It is seen from the results that the finite element failure behavior indicates a good agreement with the experimental failure behavior.     

Creep effect on the behavior of concrete beams reinforced with GFRP bars subjected to different environments

The effect of different environmental conditions on the creep behavior of concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars under sustained loads is investigated. This is achieved through testing concrete beams reinforced with GFRP bars and subjected to a stress level of about 20–25% of the ultimate stress of the GFRP bars. Reference beams were loaded in the temperature-controlled laboratory (24 ± 3 °C). Other test beams were either completely or partially immersed in different environments (tap-water and sea-water) at elevated temperature (40 ± 2 °C) to accelerate the reaction. During the exposure period, which lasted for ten months, strains in concrete and GFRP bars as well as the midspan deflections were recorded for all considered environmental conditions. The results show that the creep effect due to sustained loads was significant for all environments considered in the study and the highest effect was on beams subjected to wet/dry cycles of sea-water at 40 ± 2 °C.     

Impact resistance of steel fibrous concrete containing fibres of mixed aspect ratio

The paper presents results of an investigation conducted to study the impact resistance of steel fibre reinforced concrete containing fibres of mixed aspect ratio. An experimental investigation was planned in which 108 plain concrete and SFRC beam specimens of size 100 × 100 × 500 mm were tested under impact loading. The specimen incorporated three different volume fractions i.e. 1.0%, 1.5% and 2.0% of corrugated steel fibres. Each volume fraction incorporated mixed steel fibres of size 0.6 × 2.0 × 25 mm and 0.6 × 2.0 × 50 mm in different proportions. The drop weight type impact tests were conducted on the test specimens and the number of blows of the hammer required to induce first visible crack and ultimate failure of the specimen were recorded. The results are presented in terms of number of blows required as well as impact energy at first crack and ultimate failure. It has been observed that concrete containing 100% long fibres at 2.0% volume fraction gave the best performance under impact loading.     

Parametrical static analysis on group studs with typical push-out tests

Group studs are known as shear connectors in steel and concrete composite structures. By now, many composite bridges have been characterized by long lateral cantilevers. The shear studs are actually under biaxial action consisting of shear force and action in light of lateral bending moment on concrete slab induced by long cantilever and passing by moving loads. Moreover, lateral bending moment may even lead to the initiation of bending-induced concrete cracks. These two situations can both affect mechanical performance of group studs. Thus, a parametrical FEM analysis was carried out, in which damage plasticity was introduced to simulate material nonlinear behavior. In the analysis, lateral bending moments respectively inducing maximum concrete crack widths of 0.1 mm and 0.2 mm, shank diameters of 13 mm, 16 mm, 19 mm and 22 mm and stud heights including 80 mm and 100 mm were parameters. It was found that mechanical behavior of group studs with large shank diameter would be less affected by biaxial action and initial bending-induced concrete cracks seemed unfavorable to stud shear stiffness. On the other hand, typical push-out tests were executed to investigate reductions of shear stiffness and shear capacity of group studs. The reliability of FEM analysis was also verified based on the tests. In addition, stud shear capacity evaluations according to several design specifications were presented. It indicated shear capacity evaluation of Eurocode 4 got a relatively large safety factor. Moreover, the applicability of these specifications for group studs on shear capacity evaluation was also discussed.     

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.     

Experimental investigation on thermal and mechanical behaviour of composite floors exposed to standard fire

This paper presents experimental investigations on the thermal and mechanical behavior of composite floors subjected to ISO standard fire. Four 5.2 m×3.7 m composite slabs are tested with different combinations of the presence of one unprotected secondary beam, direction of ribs, and location of the reinforcement. The experimental results show that the highest temperature in the reinforcements occurs during the cooling phase (30–50 °C increment after 10-min cooling). The temperature at the unexposed side of the slabs is below 100 °C up to 100-min heating, compared to the predicted fire resistance close to 90 mins from EC4. For the slabs without secondary beams, the cracks first occur around the boundaries of the slab, while for the slabs supported by one unprotected secondary beam, concrete cracks first occur on the top of the slab above the beam due to the negative bending moment, and later on develop around boundaries. Debonding is observed between the steel deck and concrete slab. The secondary beam significantly impacts the deformation shape of tested slabs. Although a large deflection, 1/20 of the span length, is reached in the tests, the composite slabs can still provide sufficient load-bearing capacity due to membrane action. The occurrence of tensile membrane action is confirmed by the measured tensile stress in the reinforcement and compressive stress in the concrete. A comparison between measured and predicted fire resistance of the slabs indicates that EC4 calculations might be used for the composite slabs beyond the specified geometry limit, and the prediction is conservative.     

Shear strength of RC beams subjected to cyclic thermal loading

The experiments were performed for assessing the influence of cyclic thermal loading on the shear strength of reinforced concrete (RC) beam specimens. One hundred eleven RC beams of 100 × 150 × 1200 mm size reinforced in tension zone with two bars of 8, 10 and 12 mm diameters were tested under four point loading. The beams were subjected to a number of thermal cycles varying from 7 to 28 cycles with peak temperature taken as 100, 200 and 300 °C. The effects of thermal cycles on the crack pattern, failure mechanism, first crack load and the shear strength of beams have been discussed. The shear strength of the beams has been found to increase by up to 10% at lower temperature cycles of 100 and 200 °C but reduces by up to 14% at higher temperature (300 °C) depending on the severity of thermal loading. The results of study emphasize the need for developing appropriate guidelines for the design of RC structural elements used in comparatively high temperature environment with cyclic thermal loading conditions.     

Experimental behaviour of RACFST stub columns after exposed to high temperatures

The experimental studies on the behaviour of recycled aggregate concrete-filled steel tube (RACFST) stub columns after exposed to high temperatures are reported in this paper. Forty specimens, including 32 RACFST stub columns and 8 normal concrete-filled steel tube (CFST) stub columns as reference, were tested, and the failure pattern, load versus strain relation and ultimate strength of the specimens were presented and analysed. Five types of concrete were produced: one reference concrete with natural aggregates, two concrete mixes with recycled coarse aggregate (RCA) replacement ratios of 50% and 100%, and two concrete mixes with recycled fine aggregate (RFA) replacement ratios of 50% and 100%. The specimens were exposed to 300 °C, 600 °C and 800 °C for 3 h. The test results showed that, due to the existence of the recycled aggregates, the post-fire performance of RACFST stub columns was lower than the corresponding normal CFST specimens under the same maximum temperature suffered, and the RACFST specimens with RCA had a better behaviour than those with RFA under the same recycled aggregate replacement ratio.     

Bond strength of deformed bars in large reinforced concrete members cast with industrial self-consolidating concrete mixture

The bond strength of reinforcing bars embedded in full-scale heavily reinforced concrete sections made with industrial self-consolidating concrete (SCC) was investigated and compared with that of normal concrete (NC). The flowability of SCC mix through the dense reinforcement was visually monitored from a transparent formwork. The bond stress was tested for bars located at three different heights (150 mm, 510 mm, and 870 mm from the bottom of the pullout specimens) and at different tested ages (1, 3, 7, 14, and 28 days). The bond stress-free end slip relationship, the top bar effect and the effect of age on bond stress was investigated in both SCC and NC pullout specimens. Bond stresses predicted based on some major codes were compared with those obtained from experiments. The results indicated that casting SCC was much faster and easier and could be done with less labor effort and no concrete blockage among the heavy reinforcements compared to NC. The results also indicated that the bond stress was slightly higher in the SCC pullout specimen compared to the NC pullout specimen. The difference was more pronounced in the top bars and at 28 days of testing.     

Diagonal shear behaviour of unreinforced masonry wallettes strengthened using twisted steel bars

The in-plane shear behaviour of URM wallettes strengthened using near surface mounted high strength twisted stainless steel reinforcement (TSNSM) was investigated and in particular, the effectiveness of the reinforcing schemes to restrain the diagonal cracking failure mode was studied. A total of 17 URM wallettes, each being 1.2 m × 1.2 m in size, were structurally tested in induced diagonal compression. Of these, 3 wallettes were tested as-built and 14 wallettes were tested after being strengthened using different patterns of TSNSM bars. Several parameters pertaining to the in-plane shear behaviour of strengthened URM walls were investigated, including failure modes, shear strength, maximum drift, pseudo-ductility, and shear modulus. It was inferred from the results that as-built tested wallettes exhibited sudden post-peak strength degradation and failed along a stepped diagonal joint crack, whilst strengthened wallettes failed along distributed diagonal cracks in a more ductile fashion and exhibited a shear strength increment ranging from 114% to 189%.     

Experimental investigation of thin-walled concrete-filled steel tube columns with reinforced lattice angle

Experimental investigation of thin-walled concrete-filled steel tube columns with reinforced lattice angle was conducted in this study. The lattice angle was designed to reinforce the concrete-filled steel tube columns by increasing the percentage of steel cross-sectional area. Column specimens having different lengths ranged from 500 mm to 3500 mm were tested. The behavior and strengths of concrete-filled steel tube columns with lattice angle were investigated. In addition, concrete-filled steel tube columns having the same size but without reinforced lattice angle were also tested for comparison. Material properties of the concrete and steel used in the test specimens were measured. The test strengths are compared with the design strengths calculated using the AISC Specification and Eurocode for the design of composite structural members. A new design method was also proposed for the concrete-filled steel tube columns with reinforced lattice angle. It is shown that the design predictions from the proposed method agree with test results well.     

Column tests of dodecagonal section double skin concrete-filled steel tubes

A series of tests on dodecagonal section double skin concrete-filled steel columns (DCS) were carried out in this study. Column specimens having different lengths ranged from 1000 mm to 3500 mm were tested. The behavior and strengths of dodecagonal section double skin concrete-filled steel columns were investigated. In addition, local bucking of inner and outer steel tubes were also investigated. Material properties of the concrete and steel used in the test specimens were measured. The test strengths are compared with the design strengths calculated using the proposed methods based on current AISC Specification and Eurocode for the design of composite structural members. The suitability of design method proposed by other researcher for circular section double skin concrete-filled steel columns for dodecagonal section specimens was also evaluated.