Composite tubes as an alternative to steel spirals for concrete members in bending and shear

Glass fibre-reinforced polymer (GFRP) tubes are compared to steel spiral reinforcement in circular concrete members with longitudinal reinforcement and prestressing, using six beam tests. Two 324 mm diameter and 4.2 m long prestressed specimens were tested in bending. Four 219 mm diameter reinforced specimens were also tested, including two 2.43 m long beams tested in bending and two 0.6 m long beams tested in shear. In each set, one specimen was essentially a concrete-filled GFRP tube, while the other control specimen included steel spiral reinforcement of comparable hoop stiffness to that of GFRP tube. The strength of control specimens was governed by crushing and spalling of concrete cover. Unlike spiral reinforcement, GFRP tubes confined larger concrete areas and also contributed as longitudinal reinforcement, leading to increases in flexural and shear strengths, up to 113% and 69%, respectively.     

Effects of various admixtures and shear keys in wood–concrete composite beams

Wood–concrete composite beams are a layered system, which essentially utilize a concrete layer in compression and a wood layer in tension. This layered system offers a way to construct or rehabilitate wood floors in historic timber structures while increasing the floors’ stiffness and load carrying capacity. This research paper investigates past problems with poor consolidation of the concrete, transverse shrinkage cracks in the concrete, swelling of the wood, moisture loss from the concrete, and the resulting reduced composite efficiency. The research presented herein describes how these problems can be mitigated and thereby increase the composite efficiency of the wood–concrete composite system. By painting the specimens with a water proofing paint, the swelling of the wood can be reduced, which helps to maintain a tight interface between the wood and concrete. To improve consolidation, a self-leveling concrete was designed with a 28-day compressive strength of 34.5 MPa and a slump of 279.4 mm. Nylon fibers and Type I steel fibers were used as admixtures to the fresh concrete to determine their effect on the composite efficiency and the reduction of shrinkage cracks. Twelve full size specimens were constructed and tested to failure. It was found that the most common mode of failure was combined bending and tension at mid span in the wood. An average composite efficiency of 83.4% was reached in the full size test specimens when placed in four point bending.     

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.     

Non-destructive evaluation of the grouted ratio of a pipe roof support system in tunneling

The pipe roof system is widely used in the New Austrian Tunneling Method (NATM) as the main support system. Thus, the integrity of the pipe roof system influences the tunnel stability. The purpose of this study is to evaluate the grouted ratio of a pipe roof system using a non-destructive method in the laboratory and in the field. In the laboratory tests, four specimens embedded in soils and five non-embedded specimens are prepared with different grouted ratios of 0%, 25%, 50%, 75%, and 100%. The steel pipes are 6 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. Field tests are conducted with two fully grouted pipes with dimensions of 12 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. The reflection method of guided waves, which are generated by a hammer impact and are measured using an acoustic emission sensor, is used for the non-destructive testing. Experimental studies demonstrate that the group velocities and the main frequencies of the guided waves decrease as the grouted ratio increases for embedded and non-embedded specimen in soils. The variation of the main frequency, however, is more significant than the variation of the group velocity. In addition, the group velocities and main frequencies of the field specimens are lower than those of the embedded specimens. This study demonstrates that the variations of the group velocity and main frequency may be used effectively to estimate the grout ratio of a pipe roof system in tunneling.     

Behavior of FRP-confined concrete after high temperature exposure

This paper presents the results of an experimental program to investigate the effect of high temperature on the performance of concrete externally confined with FRP sheets. For this purpose, a two-phase experimental program was conducted. In the first phase, 42 standard 100 × 200 mm concrete cylinders were prepared. Out of these specimens, 14 cylinders were left unwrapped; 14 specimens were wrapped with one layer of CFRP sheet; and the remaining 14 specimens were wrapped with one layer of GFRP sheet. Some of the unconfined and FRP-confined specimens were exposed to room temperature; whereas, other cylinders were exposed to heating regime of 100 °C and 200 °C for a period of 1, 2 or 3 h. After high temperature exposure, specimens were tested under uniaxial compression till failure. The test results demonstrated that at a temperature of 100 °C (a little more than the glass transition temperature (T_g) of the epoxy resin), both CFRP- and GFRP-wrapped specimens experienced small loss in strength resulting from melting of epoxy. This loss of strength was more pronounced when the temperature reached 200 °C. In the second phase of the experimental program, three 100 × 100 × 650 mm concrete prisms were prepared and then overlaid by one layer of CFRP and GFRP laminates for conducting pull-off strength tests as per ASTM D4541 – 09. The objective of this testing was to evaluate the degradation in bond strength between FRP and concrete substrate when exposed to elevated temperature environments. One prism was exposed to room temperature whereas the other two specimens were exposed to heating regime of 100 °C and 200 °C for a period of 3 h. It was concluded that a significant degradation in the bond strength occurred at a temperature of 200 °C especially for CFRP-overlaid specimens.     

Effects of impregnation with Imersol-aqua on the modulus of elasticity in bending of laminated wood materials

The aim of this study was to investigate the impacts of impregnation with Imersol-aqua on the modulus of elasticity in bending (MOE) of some laminated wood materials. For this aim, oriental beech (Fagus orientalis Lipsky), oak (Quercus petrea Liebl.), Scotch pine (Pinus sylvestris Lipsky), oriental spruce (Picea orientalis Lipsky) and Uludağ fir (Abies bornmülleriana Lipsky) wood materials impregnated with Imersol-aqua according to ASTM D 1413-99 and producers’ definition. Laminated wood samples were produced from impregnated wood materials according to TS EN 386 in the five ply form (4 mm each) from oriental beech, oak, Scotch pine, Uludağ fir and oriental spruce wood by using Desmodur-VTKA adhesive. The MOE values were measured according to TS EN 408. Consequently, the MOE of impregnated + laminated (I + L_W) softwoods, pine, spruce and fir increased, respectively by 8.07%, 2.62% and 2.45% whereas the MOE of laminated + laminated hardwoods, beech and oak decreased, respectively by 5.06% and 4.37% with respect to laminated control samples (L_W). Considering the interaction of wood type and process, the MOE was obtained from laminated oriental beech, whereas the lowest was found for impregnated Uludağ fir. In consequence, in the massive construction and furniture elements that the MOE after the impregnation and lamination (I + L_W) is of great concern, oriental beech and Scotch pine materials could be recommended.     

Resistance of flush endplate connections under tension and shear in fire

This paper presents an experimental and numerical study to the resistance of flush endplate connections in fire. Six transient fire tests were performed on two types of connections with flexible and stiff endplate. For each connection, three load combinations were tested and the test results were reported. The test shows that most connections failed within the range of 500 °C to 650 °C. Extreme bending deformation of the endplate and flexural deformation of the bolt were observed when the plate thickness was 8 mm. When the endplate thickness became 16 mm, deformations occurred to the column flange and the bolts as the endplate became thicker than the column flange. Connection fire resistances were found to decrease with increase of either tension or shear, but the connection deformations were similar regardless of the load combination within the range tested. The three-dimensional finite element simulations of the tests with flush endplate connections were conducted with general-purpose finite element program ABAQUS. The results obtained from analysis showed a good agreement with the experimental responses. Parametric study was performed to the connection failure mechanisms under an extensive range of load combinations of tension and shear in fire using the finite element model. Conclusions were drawn regarding the tension and shear interactive relationships for the two typical connections at different temperatures.     

Study of full-scale elements of a ferrocement roof system for Caribbean application

The Caribbean region is exposed to hurricanes annually and the frequency of occurrence is expected to increase due to global warming. However, as revealed due to hurricane Ivan in 2004, the current roofing systems of the houses are particularly vulnerable. In other parts of the world ferrocement roofing is a technically and economically viable solution but for acceptance in the Caribbean, the aesthetic factor controls the roof design in terms of topology prompting a new innovative solution. Load test data is also required by the approving agencies of the various jurisdictions in the Caribbean. The results of structural testing of the full-scale main components of a proposed ferrocement roof system are presented. This comprises of a 9.0 m wide and 2.5 m high pitched-portal frame of channel-section with bolted steel connections; a 6.10 m hollow-section roof slab in bending, and slab-to-frame bolted connections in pullout. It was found that the performance of the elements is consistent with the acknowledged beneficial behavior of ferrocement, and the proposed ferrocement roof system should adequately address the loading conditions expected in the Caribbean. The data can also be used to determine safe spans of the proposed roof system for application in other regions as well.     

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.     

Flexural response of hybrid carbon fiber thin cement composites

It is evident that the carbon-fiber-reinforced cementitious composites are being used in the structural and construction works owing to the synergetic action from two components viz. fiber and mortar matrix. Incorporation of a very nominal percentage of carbon fibers into a mortar mixture produces a strong and durable composite that leads the product of smart material properties. Flexural behavior of cement-based matrices carrying carbon fibers reinforcement of different percentage and size is studied in this paper. Influence of fiber content and length of the fiber is quantified using load–deflection curves. Specimens containing fiber of 0.0, 0.5, 1.0 and 1.5% with 3 mm (0.12 in.), 6 mm (0.36 in.), and their combination are prepared and tested. It is demonstrated that combination of 3 mm (0.12 in.) and 6 mm (0.36 in.) fibers enhances the bearing capacity to crack- and ultimate-stresses as well as the Young’s modulus of the fiber reinforced cement composites. The paper emphasizes the desired performances after the initiation of cracks and discusses the pre- and post-cracking load–deflection characteristics of the composites.     

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.     

Repair of heat-damaged reinforced concrete slabs using fibrous composite materials

Sixteen under-reinforced high strength concrete one-way slabs were cast, heated at 600 °C for 2 h, repaired, and then tested under four-point loading to investigate the coupling effect of water recuring and repairing with advance composite materials on increasing the flexural capacity of heat-damaged slabs. The composites used included high strength fiber reinforced concrete layers; and carbon and glass fiber reinforced polymer (CFRP and GFRP) sheets. Upon heating then cooling, the reinforced concrete (RC) slabs experienced extensive map cracking, and upward cambering without spalling. Recuring the heat-damaged slabs for 28 days allowed recovering the original stiffness without achieving the original load carrying capacity. Other slabs, recured then repaired with steel fiber reinforced concrete (SFRC) layers, regained from 79% to 84% of the original load capacity with a corresponding increase in stiffness from 382% to 503%, whereas those recured then repaired with CFRP and GFRP sheets, regained up to 158% and 125% of the original load capacity with a corresponding increase in stiffness of up to 319% and 197%, respectively. Control, heat-damaged, and water recured slabs showed a typical flexural failure mode with very fine and well distributed hairline cracks, propagated from the repair layers to concrete compression zone. RC slabs repaired with SFRC layers failed in flexural through a single crack, propagated throughout the compression zone, whereas those repaired with CFRP and GFRP experience yielding failure of steel prior to the composites failure.     

Mechanical properties of concrete produced with a composite of water treatment sludge and sawdust

In developing countries such as Brazil, the wastes generated in the decanters and filters of water treatment plants are discharged directly into the same rivers and streams that supply water for treatment. Another environmental problem is the unregulated discard of wood wastes. The lumber and wood products industry generates large quantities of this waste, from logging to the manufacture of the end product. Brazil has few biomass plants and therefore only a minor part of these wastes are reused. This paper presents the results of the first study involving a novel scientific and technological approach to evaluate the possibility of combining these two types of wastes in the production of a light-weight composite for concrete. The concrete produced with cement:sand:composite:water mass ratios of 1:2.5:0.67:0.6 displayed an axial compressive strength of 11.1 MPa, a compressive and diametral tensile strength of 1.2 MPa, water absorption of 8.8%, and a specific mass of 1.847 kg/m³. The mechanical properties obtained with this concrete render it suitable for application in non-structural elements.     

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.     

Impacts of impregnation chemicals on combustion properties of the laminated wood materials produced combination of beech and poplar veneers

The aim of this study was to investigate the effects of impregnation with boron compounds Borax (B_X), Boric acid (B_A), B_X + B_A, Imersol-Aqua (I_AQUA) and Timbercare-Aqua (T_AQUA) on combustion properties of the laminated wood materials produced combination of Oriental beech and poplar veneers bonded with Desmodur-VTKA (D_V) and Poly(vinyl acetate) (P_VAc) adhesives. The test samples, prepared from beech (Fagus orientalis Lipsky) and poplar (Populus nigra Lipsky) woods, were impregnated boron compounds by vacuum, I_AQUA by dipping and T_AQUA by brushing methods according to ASTM D 1413-76-99 and directions of the manufacturer. The laminated wood materials were prepared in the form of five layers, 4 mm thickness from the impregnated beech and poplar veneers according to TS EN 386. Combustion properties of samples after laminated and impregnated process were determined according to ASTM E 160-50. Considering the interaction of combustion type and impregnation materials, combustion temperature was found the highest in flame source combustion (F_SC) + T_AQUA (528.150 °C) but the lowest in without flame source combustion (WF_SC) + B_A (391.333 °C). Consequently, boron compounds and I_AQUA showed a decreasing impact on combustion properties of the laminated wood materials, produced combination of beech and poplar veneers, bonded with D_V. In consequence, impregnation with boron compounds and Imersol-Aqua of the laminated wood materials, bonded with Desmodur-VTKA, provides security for the usage of having high risk of fire.     

Performance of CFTST column to steel beam joints with blind bolts under cyclic loading

The objective of this research is to investigate the seismic performance of the composite joint consisting of square concrete filled thin-walled steel tubular (CFTST) column and steel beam with end plate and blind bolts. The cold-formed square tube in each CFTST column connection was fabricated by seam welding together four pieces of lipped angle with nominal wall thickness 1.5 mm or 3 mm. Four exterior joint specimens were tested under axially compressive load on the top of the columns and cyclic loads on the beam tip. The experimental parameters in the study were the thickness of the steel tube and the type of end plate. The seismic response of the blind bolted moment joints to CFTST columns was analyzed and evaluated in terms of the hysteretic behavior, failure modes, stiffness and strength degradation, ductility, and energy dissipation capacities of the joints. To improve the tension behavior of the blind bolted moment connections to the thin tube wall, the anchorage action of reinforcing rebar welded to the bolts with concrete-filled steel tubes was also investigated to consider the effect of cyclic loading. The experimental and analytical results indicated that when the end plate thickness is not less than 3 mm, the flush or extended end plate joints to CFTST columns exhibited large hysteretic loops and excellent seismic performance, such as ductility and energy dissipation capacity. The proposed innovative blind bolted joint was verified as a reliable and effective solution applied in mid- and low-rise buildings through properly design and detailing.     

Monitoring the energy-use effects of cool roofs on California commercial buildings

Solar-reflective roofs stay cooler in the sun than solar-absorptive roofs. Such “cool” roofs achieve lower surface temperatures that reduce heat conduction into the building and the building's cooling load. We monitored the effects of cool roofs on energy use and environmental parameters in six California buildings at three different sites: a retail store in Sacramento; an elementary school in San Marcos (near San Diego); and a four-building cold storage facility in Reedley (near Fresno). The latter included a cold storage building, a conditioning and fruit-palletizing area, a conditioned packing area, and two unconditioned packing areas.Results showed that installing a cool roof reduced the daily peak roof surface temperature of each building by 33–42 K. In the retail store building in Sacramento, for the monitored period of 8 August–30 September 2002, the estimated savings in average air conditioning energy use was about 72 Wh/m²/day (52%). On hot days when the afternoon temperature exceeded 38 °C, the measured savings in average peak demand for peak hours (noon–5 p.m.) was about 10 W/m² of conditioned area. In the school building in San Marcos, for the monitored period of 8 July–20 August 2002, the estimated savings in average air conditioning energy use was about 42–48 Wh/m²/day (17–18%). On hot days, when the afternoon temperature exceeded 32 °C, the measured savings in average peak demand for hours 10 a.m.–4 p.m. was about 5 W/m² of conditioned area. In the cold storage facility in Reedley, for the monitored period of 11 July–14 September 2002, and 11 July–18 August 2003, the estimated savings in average chiller energy use was about 57–81 Wh/m²/day (3–4%). On hot days when the afternoon temperature exceeded 38 °C, the measured savings in average peak-period demand (average cooling-power demand during peak demand hours, typically noon–6 p.m.) was about 5–6 W/m² of conditioned area.Using the measured data and calibrated simulations, we estimated savings for similar buildings installing cool roofs in retrofit applications for all 16 California climate zones. For similar retail stores in climate zones 2 and 4–16, installing a cool roof can save about 6–15 kWh/m²/year of conditioned area. In climate zones 2–16, estimates of average peak demand savings for hours noon–5 p.m. range from 2.9 to 5.8 W/m². For similar school buildings in climate zones 2–16, installing a cool roof can save from 3 to 6 kWh/m²/year of conditioned roof area. For all 16 climate zones estimates of average peak demand savings for hours noon–5 p.m. range from 2.6 to 3.8 W/m². In similar cold storage buildings in all 16 climate zones, installing a cool roof can save about 4.5–7.4 kWh/m²/year of conditioned roof area. In all 16 climate zones, estimates of average peak demand savings for hours noon–5 p.m. range from 3.9 to 6.6 W/m².     

Long-term bond performance of GFRP bars in concrete under temperature ranging from 20 °C to 80 °C

Eighty pull-out specimens were used to study the effect of temperature ranging from 20 °C to 80 °C in dry environment on bond properties between Glass Fiber Reinforced Polymer (GFRP) bars and concrete. The pullout-test specimens were subjected during 4 and 8 months to high temperatures up to 80 °C and then compared to untreated specimens (20 °C). Experimental results showed no significant reduction on bond strength for temperatures up to 60 °C. However, a maximum of 14% reduction of the bond strength was observed for 80 °C temperature after 8 months of thermal loading. For treated specimens, the coefficient β in the CMR model, which predicts the bond–stress–displacement behavior, seems to be dependant with the temperature.     

Abrasion resistances of cellulosic,synthetic, polyurethane,waterborne and acidhardening varnishes used woods

This study was performed to determine the abrasion resistances of some varnishes used on wood materials. For this purpose, test samples prepared from Scots pine, Oriental beech, European oak, Black poplar, Basswood and Black walnut woods, which met the requirements of ASTM D 358, were coated according to ASTM D 3023 standards with cellulosic (C), synthetic (Sn), polyurethane (Pu), waterborne (Wb) and acidhardening (Ah) varnishes. The abrasion resistance of samples after the varnishing process was determined in accordance with TS 4755. It was observed that, according to wood samples, the highest abrasion resistance was obtained in Black walnut (168.9 rpm), and the lowest abrasion resistance was obtained in Scots pine (50.63 rpm); according to varnish types, the highest abrasion resistance was obtained in acidhardening (213.4 rpm), and the lowest abrasion resistance was obtained in waterborne (45.44 rpm). In accordance with the interaction of the factors wood type, varnish type and layer type, the highest abrasion resistance was found at interaction of Black walnut + acidhardening + 3 layers (578.0 rpm), and the lowest abrasion resistance was found at interaction of Oriental beech + waterborne + 1 layer (11.50 rpm). Furthermore, it was found that interactions according to the varnish type and amount of layer thickness display differences; varnish types are efficient to the first degree and layer thickness to the second degree for abrasion resistance. In this respect, it can be stated that in wooden parquets and place floorings, in which the abrasion resistance is considerably important, the varnish application with three layers of acidhardening can provide an advantage.