Concrete Topping Research Articles

Restraint Moments in Bridges with Full-Span Prestressed Concrete Form Panels

An experimental investigation was carried out to evaluate the restraint moments generated at interior piers of bridges constructed with full-span prestressed concrete form panels. These moments result from the restraint of time-dependent deformation after adjacent spans are made continuous through a composite cast-in-place concrete topping. The experimentally determined moments from this investigation were compared with values calculated using current design methods for continuous prestressed concrete girders. It was concluded that these design methods, which ignore cracking of the cast-in-place topping, greatly overestimate the negative restraint moments in composite construction with shallow prestressed members. A new method for calculating restraint moments in bridges with shallow prestressed members, which includes provisions for cracking, is presented. Numerical design examples are included to illustrate the proposed method.

Fatigue Response of Concrete Decks Reinforced with FRP Rebars

The fatigue response of concrete decks reinforced with fiber-reinforced plastic (FRP) bars is critical to the long-term endurance of this type of innovative structure. To evaluate the degradation of FRP reinforced bridge decks, fatigue tests were conducted on four concrete deck steel stringers. An initial stress range of 2.27 MPa (0.33 ksi) (tension) in the main FRP reinforcement, 3.1 MPa (0.45 ksi) (compressive) in the concrete deck top, and 24.8 MPa (3.6 ksi) (tension) at the bottom flange of a steel stringer was applied for all specimens. The stringer stiffness, composite versus noncomposite casting, and transverse posttensioning using high-strength Dywidag steel rods were varied during this research. The fatigue test results showed no loss of bond between FRP rebars and concrete in any of the test specimens. The major crack patterns were in the direction parallel to the stringers, i.e., flexural cracks in the concrete deck spanning the steel stringers. Effective central deck deflections could be set as a measure of global deck degradation during fatigue, and this rate of degradation in decks reinforced with FRP rebars was found comparable to decks reinforced with steel rebars.

Composite Slab Construction Utilizing Carbon Fiber Reinforced Mortar

This paper reports an experimental research program focused on studying composite floor systems consisting of carbon fiber mortar deck reinforced with steel bars and plain concrete topping. Mix design and manufacturing techniques for carbon fiber reinforced mortar were optimized based on Ref 1 to 4. Variables of the experimental program were the steel reinforcement ratio, and the thickness of carbon fibrous mortar Ten prototype composite specimens were constructed and tested in flexure under one-third point loading. The test results indicated that the proposed composite system exhibited comparable flexural load-deflection behavior compared to conventional reinforced concrete. With increasing steel reinforcement ratio, increase in flexural strength and toughness was achieved. No significant effect on flexural behavior was detected by reasonably reducing the thickness of carbon fiber mortar deck. Delamination (interfacial bond failure) between the carbon fiber mortar deck and the concrete topping was a dominant mode of failure. Use of shear keys is warranted for further research efforts on this topic.

A Composite Precast Prestressed Concrete System for Marine Wharfs

This article describes the concept and application of a composite precast, prestressed concrete system for wharfs in marine areas. The precast system comprises piles, beams, and a composite slab with a cast-in-place concrete topping. The resulting structure is functional, has strength, long-term durability, economy and can be erected quickly. Design-construction highlights of the project are discussed.

Deformations in Composite Prestressed Concrete Bridge Deck Panels

Prestressed concrete (PC) panels have been periodically used as permanent formwork in bridge deck construction for over 35 years. To investigate the behavior of this composite slab system at locations adjacent to abutment and pier diaphragms in skewed bridges, five full‐scale composite slab specimens were constructed and tested. Slab performance was evaluated by investigating the initial strand transfer length, monitoring the prestressing strands for slippage at the ends of the PC panels, detecting degradation of the composite behavior between PC panels and a reinforced concrete topping slab within and at the end of a span, and establishing the distribution of the bending strains along the specimen lengths. The experimental results revealed that the initial strand transfer length for bare (uncoated), 9.52‐mm (,3/8‐in.) diameter, seven‐wire, low‐relaxation prestressing strands was about 724 mm (28.5 in.) and that slippage of the prestressing strands and degradation of full‐composite behavior did not occur during the service or factored level load tests. Each composite slab specimen had a substantial amount of reserve strength remaining after initial strand slippage and initial breakdown of full‐composite behavior were detected. The measured PC panel compressive strains, induced during prestressing, and the monitored slab bending strains, caused by wheel footprint loads, compared well with the result predicted by simplified finite‐element analyses of the specimens.

Tests on Special Reinforcement for the End Support of Hollow-Core Slabs

90 Details of special reinforcement at the end supports of hollowcore precast concrete floor units with a cast-in-place concrete topping slab are discussed. This reinforcement is intended to prevent collapse of the floors in the event of inadequate seating lengths or imposed movements due to volume changes or earthquakes. Results from experimental tests in which a vertical load was applied to the hollow-core precast concrete floor units with a cast-in-place topping slab and special support reinforcement are also presented. Three types of special reinforcement were investigated with two types of test. In one test, the vertical load was applied when the support seating was zero; in the other test, the vertical load was applied after the precast floor unit had been pulled horizontally off the supporting beam. The special reinforcement was shown to be capable of supporting at least the service gravity loads in these extreme conditions, if well designed.

Solar thermal analysis of honeycomb roof cover system for energy conservation in an air-conditioned building

Periodic analysis of solar heat transfer processes in a system comprising an air-filled honeycomb placed on the concrete roof top of an air-conditioned building was carried out to investigate solar thermal gain and assess the effectiveness of system components. An explicit expression for the heat flux entering the indoor space is derived. Results of calculations corresponding to a typical winter day at Boulder, USA, (40°N) show that the solar gain (heat flux) of the system increases with the depth of honeycomb and a panel of depth 10–15 cm seems optimum for such an application.

Shear Strength of Precast Prestressed Hollow Slabs with Concrete Topping

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Measurement and interpretation of loading tests of concrete top blocks on soft ground : Arai, K; Ohnishi, Y; Horita, M; Yasukawa, I Proc 2nd International Symposium on Field Measurements in Geomechanics, Kobe, 6–9 April 1987V2, P1177–1184. Publ Rotterdam: A A Balkema, 1988

Measurement and interpretation of loading tests of concrete top blocks on soft ground : Arai, K; Ohnishi, Y; Horita, M; Yasukawa, I Proc 2nd International Symposium on Field Measurements in Geomechanics, Kobe, 6–9 April 1987V2, P1177–1184. Publ Rotterdam: A A Balkema, 1988

Punching shear of steel-concrete open sandwich slabs

Synopsis An experimental programme was conducted on simply supported, two-way epoxy-bondedsteel-concrete open sandwich slabs under a central patch load. The major parameters of the study were the method of surface preparation for the steel plate, size of patch load, grade of concrete and thickness of concrete topping. The results of twelve slabs tested in this programme are presented and discussed. On the basis of the test data, a modijication to the existing plastic theory for conventional reinforced concrete is suggested for the design of open sandwich slabs against punching shear failure.

Investigation of prestressed concrete box beams of an elevated expressway

The object of this paper is to share the experience gained from an investigation of prestressed concrete box beams of the elevated roadway of the F. G. Gardiner Expressway in Toronto, 16 years after construction. The 18–30 m long, simply supported beams, which are either pretensioned or posttensioned with prestressing strands, are covered by concrete topping and asphalt. Methods of investigation include coring, chloride-content tests, and power chipping of soffit areas. Rusted reinforcing steel, rusted prestressing strands, and delaminated or spalled concrete were found at transverse joints and at beam soffits. Concrete damage due to bird droppings, as well as a beam with nearly 60% strand loss, were discovered. Causes for deterioration are discussed and proposed repair methods are described.

Constitutive equations for engineering materials

The Cross-Laminated Timber (CLT) concrete composite floor can successfully address the issues of conventional wood product and become an attractive alternative material for conventional reinforced concrete floors in mid to high-rise building. The purpose of this research was to fully evaluate the capacity of this novel hybrid composite material under both dynamic and static conditions, before such this hybrid system becomes widely employed. This was achieved by performing a full-scale testing of five floor specimens. One specimen was designed according to Eurocode 5 to satisfy the design load for common office buildings, and four specimens were prepared with a concrete topping with different connector types, connector angles, and connector spacing. The test results illustrated that the CLT–concrete floor specimens had excellent structural performance in terms of strength capacity, 3 –5 times higher than the conventional CLT floor. The vibration performances of this composite floors were also enhanced, resulting in a remarkably effective use of this innovative materials.

PERFORMANCE OF PRECAST PRESTRESSED HOLLOW CORE SLAB WITH COMPOSITE CONCRETE TOPPING

This load test of a machine-made hollow-core slab with composite topping verified a number of accepted industry design and fabrication practices, specifically the following: 1. Impact test hammer data taken on the side of the member provided an accurate assessment of concrete strength as determined by uncracked deflection behavior and ultimate moment capacity. 2. The observed ultimate moment was about 10 percent greater than calculations based on Eq.(18-3) in ACI 318-71 but nearly identical to calculations based on strain compatibility by Fig. 5.2.5 in the PCI Design Handbook. 3. The bilinear concept for predicting the deflection of cracked prestressed members was conservative well beyond a nominal bottom fiber tensile stress of 12i,/ f'c. 4. Composite action between the precast and cast-in place portions was evident up to ultimate load. The top surface of the precast slab was a smooth, even, machine cast finish and did not comply with Section 17.7 of ACI 318-71. There was no reinforcing steel projecting from the precast slab into the topping concrete. 5. A shear failure did not occur even though the ultimate shear stress vu was 1.75 times vc as computed in accordance with ACI 318-71.