Douglas Cleary

Effect of Elevated Temperatures on a Fiber Composite Used to Strengthen Concrete Columns

Externally applied composite reinforcement can be used to provide additional strength or ductility to concrete members as part of a seismic retrofit or repair to a structure, but the composite reinforcement may be exposed to elevated temperatures. In this study, concrete cylinders were wrapped with a composite reinforcing system, exposed to a range of elevated temperatures and allowed to cool. Subsequent compression testing of the cooled cylinders indicated there was no statistically significant loss of strength until the treatment temperature was more than 30°C above the glass transition temperature of the epoxy. Additionally, the predominant mode of failure of the composite system changed from hoop split to seam debonding at the same temperature. This study also examined the role of a fire-protective coating that forestalled the onset of the transition of failure modes by almost 30°C.

BOND STRENGTH OF EPOXY-COATED REINFORCEMENT

The paper presents results of recent tests of concrete members reinforced with epoxy-coated bars. Evaluation of the bond strength, member defelections, and crack width and spacing are included. Recommendations for further research are made.

THE PERFORMANCE OF EPOXY-COATED SHEAR REINFORCEMENT

This paper examines the performance of epoxy-coated stirrups in reinforced concrete beams under bending and shear. A review of previous studies in bond and detailing of stirrups is provided. The results of an experimental program are described. From these results, several conclusions are reached, supported by ultimate failure load, deflection, stirrup strain, crack pattern, and crack width data. All beams reinforced with epoxy-coated stirrups and those with uncoated stirrups failed at higher than calculated shear capacities from those in American Concrete Institute (ACI) 318-89 and the proposed American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) 1993 Bridge Specifications.

Ultrasound inspection of wastewater concrete pipelines—signal processing and defect characterization

This paper focuses on the development of an innovative nondestructive test procedure (system+algorithm) for characterizing defects in concrete sewer pipelines, using ultrasonic inspection. A signal processing technique is being developed that is invariant to changes in both concrete material properties and composition of wastewater. Development of such an inspection procedure will be the first step in the design of a mobile autonomous vehicle for inspecting wastewater pipeline systems. Results demonstrating the validity of the proposed approach are presented.

PERFORMANCE OF CONCRETE BRIDGE DECKS AND SLABS REINFORCED WITH EPOXY-COATED STEEL UNDER REPEATED LOADING

To evaluate the structural performance of concrete bridge decks and slabs with epoxy-coated reinforcement and subjected to repeated loading, investigators tested 34 slab specimens of two types of cross section with splices and transverse steel. Evaluations were performed by comparing the performance of specimens with uncoated bars to that of otherwise identical companion specimens with epoxy-coated bars under repeated loading and at ultimate load condition. Test variables included concrete compressive strength, bar size and deformation pattern, coating thickness, splice length, and applied stresses. During the repeated loading portion of the tests, specimens with epoxy-coated reinforcement had fewer but wider cracks than those with black reinforcement, while differences in deflections were not significant. Average bond stress ratios were 0.78 with #7 bars and 0.75 with #11 bars at failure. The strength results support the use of a single development length modification factor for beams with spliced epoxy-coated reinforcement.

EPOXY-COATED REINFORCEMENT UNDER REPEATED LOADING

Twenty three beams with splices placed in a constant moment region were subjected to repeated loading and then tested to failure to compare the service and ultimate load behavior of beams with coated and uncoated reinforcement. The repeated loading consisted of one million or 5 million cycles in the service load range. Splittng cracks formed at a lower load in beams with epoxy-coated reinforcement than in beams with uncoated reinforcement. Deflections, crack widths, and reinforcement stresses were larger in beams with epoxy-coated reinforcement during service loading. The differences were reduced with repeated loading. The differences are attributed to a larger friction component of the bond mechanism with uncoated reinforcement.

Load Transfer Efficiency of Rigid Airfield Pavement: Relationship to Design Thickness and Temperature Curling

FAA uses a mechanistic design procedure, FAA Rigid and Flexible Iterative Elastic Layer Design (FAARFIELD), for the design of rigid airport pavements. FAARFIELD does not consider curling stresses in determining the portland cement concrete (PCC) layer thickness and assumes constant stress-based load transfer efficiency [LTE (S)] of 0.25 at the joints. Recently completed studies have shown that LTE (S) values under moving aircraft loads can be significantly higher than 0.25. In addition, the curling stresses, induced because of the temperature differentials at the top and bottom of the PCC slab, can affect the load transfer efficiency at the joint. Higher curling stresses can lead to higher combined stresses (loading plus curling) in pavements. The objective of this study is to analyze the effect of load transfer efficiency and loading intensity on PCC design thickness and the effect of PCC temperature gradient on LTE (S) and critical edge stresses. The results indicate that for a slab that shows no curling, an increase in LTE (S) value by 0.10 would reduce the PCC design thickness by 1.3 in. (33 mm) under FAA design procedures. In addition, when the top of the slab has a higher temperature than does the bottom of the slab, higher stresses at the joint and higher LTE (S) are observed. The variations in temperature gradient induce curling stresses in the slab and affect the LTE (S) at the joints.

Load-Transfer Efficiencies of Rigid Airfield Pavement Joints Based on Stresses and Deflections

The objective of this study is to obtain and compare stress based load transfer efficiency [LTE(S)] and deflection based load transfer efficiency [LTE(d)] of rigid pavement airfield joints measured during the full scale testing of airfield pavements at the Federal Aviation Administrations (FAA’s) National Airport Pavement Test Facility (NAPTF). FAA current rigid pavement thickness design procedure assumes LTE(S) of 25% as an aircraft traverses a joint. Since, it is not convenient or practical to measure LTE(S) in field, the current FAA specification determines LTE(S) from LTE(d) which suggest that LTE(S) of 25% is equivalent to LTE(d) of 70-90%. Falling weight deflectometer (FWD) generally serves the purpose of measurement of deflections and LTE (d). However, the equivalency of LTE(d) and LTE(S) depends on the effect of single plate loads of FWD versus multiple gear loads of aircraft and short duration impulse loads of FWD verses a comparatively longer duration dynamic aircraft wheel loading. The paper presents the results of the analysis from FWD and slow moving wheel load tests. The results showed that the deflection based load transfer efficiency was similar between single wheel loading and 4-wheel loading. However, a noticeable difference in the value of LTE(S) was observed between 4-wheel static load and 4-wheel moving load. The study thus infers that the commonly used correlation for estimating LTE(S) from LTE(d) measured by FWD is valid only for static load. The same correlation significantly underestimates the LTE(S) of dowelled joints under moving aircraft loads.

Steel Connections with Fiber-Reinforced Resin Thermal Barrier Filler Plates under Service Loading

AbstractFiber-reinforced resin (FRR) plates are being incorporated into structural joints to correct thermal bridging issues to create more energy-efficient buildings. The purpose of this study was to evaluate the behaviors of simple shear and moment connections that include FRR thermal barrier plates under service-loading conditions. Tests included two thicknesses and two grades of barrier plate. The shear connection tests showed that the coefficient of friction between steel and an as-received FRR plate was significantly lower than that of steel on steel. However, roughening the FRR plates by blasting with aluminum oxide increased the coefficient to nearly the same as or greater than steel on steel. In moment connections the presence of thermal barrier plates increased the joint rotation at the connection. A 25-mm (1-in.) thermal barrier plate increased the joint rotation by 10% compared to a joint without the barrier plate. The increase was 20% for a 50-mm (2-in.) plate. The thermal barrier plates did ...

Impact of dynamic loading on backcalculated stiffness of rigid airfield pavements

The objective of this paper was to evaluate the deterioration of Portland Cement Concrete (PCC) slabs throughout trafficking. A full-scale accelerated pavement testing at the National Airport Pavement Test Facility (NAPTF) was conducted on Construction Cycle 6 (CC6) on rigid pavements with low, medium and high flexural strengths on both a concrete and asphalt stabilised base. Heavy Weight Deflectometer (HWD) testing was conducted on the test sections to backcalculate the stiffness of the layers. The majority of PCC deterioration occurred roughly within the first 1500–2000 passes of trafficking. On average, the MRS-1 (low flexural strength) PCC elastic modulus was found to decrease by 20%, from 5.0–.4 × 106 (34.5–37.2 GPa) to 4.0–4.3 × 106 psi (27.6–29.7 GPa), whereas the PCC elastic modulus of MRS-2 and MRS-3 was found to decrease by 17% and 22%, respectively. However, neither the MRS-2 nor MRS-3 elastic modulus was found to drop below 5.0 × 106 psi (34.5 GPa) after 15,000 passes.