Behavior of Hollow-Core Composite Bridge Columns having Slender Inner Steel Tubes

This paper experimentally investigates the seismic behavior of three large-scale hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) columns. An HC-FCS column consisted of a concrete shell sandwiched between an outer glass fiber-reinforced polymer (GFRP) tube and an inner steel tube. Both tubes provided continuous confinement for the concrete shell along with the height of the column. The columns had two different steel tube diameter-to-thickness (Ds/ts) ratios of 85, and 254. Each steel tube was embedded into the footing, with an embedded length of 1.25-1.6 times its diameter, while the GFRP tube was not embedded into the footing. Two columns were tested as as-built specimens. Then, one of these columns was repaired and re-tested. This study revealed that HC-FCS columns having a high Ds/ts ratio of 254 and short embedded length (1.25 Ds) do not dissipate high levels of energy and display nonlinear elastic performance due to severe steel tube buckling and slippage. However, the column with a Ds/ts ratio of 85 combined with substantial embedment length (1.6 Ds) results in a nonlinear inelastic behavior, high-energy dissipation, and ductile behavior. A retrofitting technique for a high Ds/ts ratio HC-FCS column precluding buckling of the inner steel tube was proposed and examined. The retrofitting method was characterized by the use of an anchorage system with steel tube concrete filling at the joint interface region. The retrofitted column achieved the ductile behavior and performed well under seismic loading with flexural strength increased by 22%. However, the lateral displacement capacity decreased by 26% compared to the original column due to the residual deformations and stresses exhibited during the previous test

Seismic Performance of Hollow-Core HC-FCS Columns having Inner Steel Tube with High Diameter to Thickness Ratio

This paper experimentally investigates the seismic behavior of a large-scale hollow-core fiber-reinforced polymer-concrete-steel HC-FCS column under seismic cyclic loading. The HC-FCS column consisted of a concrete shell sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The FRP tube provides continuous confinement for the concrete shell along the height of the column while the steel tube provides the required flexural strength. The tested column has an inner steel tube that had a diameter-to-thickness ratio (Di/t) (of 254. The seismic performance of the precast HC-FCS column was compared to that of HC-FCS column having(Di/t) of 64. Three-dimensional numerical models were also developed using LS_DYNA software for modeling the HC-FCS columns. This study revealed that HC-FCS columns having very high (Di/t) and short embedded lengths do not dissipate high levels of energy and display nonlinear elastic performance due to steel tube slippage. However, the use of small values of (Di/t)combined with generous embedment length results in a nonlinear inelastic behavior, high energy dissipation, and ductile behavior

Inelastic Response Evaluation of Precast Composite Columns under Seismic Loads

This paper presents a non-linear finite element analysis of large-scale hollow-core fiber-reinforced polymer-concrete-thin walled steel (HC-FCS) precast columns under reversed cyclic loading. The HC-FCS columns provide an economical and efficient alternative to conventional concrete bridge columns. The precast HC-FCS column consists of a concrete shell sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner thin-walled steel tube. The steel tube diameter-to thickness (Di/ts) ratio was 254. The proposed FEA model was developed using LS_DYNA multipurpose software and was verified by experimental results performed in this study. The FE model was used to investigate some important phenomena such as thin-walled steel tube cyclic local buckling and to determine where and when steel tube yielding and damage initiation occurs. The comparison and analysis of the proposed model to predict local damages, failure patterns, and hysteretic curves were in reasonable accuracy with the experimental outcomes

Seismic Performance of Hollow-Core Composite Columns under Cyclic Loading

This paper experimentally investigates the seismic behavior of a large-scale, hollow-core, fiber-reinforced, polymerconcrete- steel HC-FCS column under cyclic loading. The typical precast HC-FCS member consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The FRP tube provides continuous confinement for the concrete wall, along the height of the column. The column is inserted into the footing and temporarily supported; then, the footing is cast in place around the column. The seismic performance of the precast HC-FCS columns was assessed and compared with previous experimental work. The compared column had the same geometric properties; but the steel tube was 25% thicker than the column that was tested in this study. This paper revealed that these HC-FCS column assemblies were deemed satisfactory by developing the whole performance of such columns and using that performance to provide excellent ductility with inelastic deformation capacity by alleviating the damage at high lateral drifts

Nonlinear Analysis of Hollow-Core Composite Building Columns

This paper numerically investigates the behavior of hollow-core fiber-reinforced polymer-concrete-steel (HC-FCS) building columns under combined axial compression and flexural loadings. The HC-FCS column for buildings consists of an outer circular fiber-reinforced polymer (FRP) tube, an inner square steel tube, and a concrete wall between them. A three-dimensional numerical model has been developed using LS_DYNA software for modeling of large scale HC-FCS columns. The nonlinear FE models were designed and validated against experimental results gathered from HC-FCS columns tested under cyclic lateral loading. The FE results were in decent agreement with the experimental backbone curves. These models subsequently were used to conduct a parametric study investigating the effects of the concrete wall thickness, steel tube width-to-thickness (B/t) ratio, and local buckling instability on the behavior of the HC-FCS columns. The obtained local buckling stresses results from the FE models were compared with the values calculated from the empirical equations of the available design codes. Finally, an approximated expression based on the available empirical formulas and the FE model results has been proposed in this paper to calculate the local buckling stresses of HC-FCS columns

Interfacial Shear Bond Strength between Steel H-piles and Polymer Concrete Jackets

Steel H-piles have been used widely in bridge construction throughout the U.S. because of their relatively large load-carrying capacity while occupying a small area. However, many H-piles suffer from corrosion, which may lead to abrupt collapse. A cost-effective repair technique, including encasing the corroded region of the steel pile into a concrete jacket, which acts as an alternative load path for the applied axial load, has been used by several state Departments of Transportation. Methyl methacrylate polymer concrete (MMA-PC) is a type of concrete that is commonly used as a repair material. However, there is limited research on the assessment of bond strength between MMA-PC and steel elements. This paper investigates experimentally the bond behavior of seven full-scale steel H-piles encased in concrete jackets. The jackets were cast using either MMA-PC or Portland cement concrete (CC). Different embedment lengths of 63.5mm (2.5 in.), 127mm (5 in.), and 190.5mm (7.5 in.) were used for the MMA-PC and one embedment length of 254mm (10 in.) was used for the CC jacket. Cylindrical and prismatic jacket configurations were used and tested using push-out. The experimental results revealed that using the MMA-PC jacket was more effective compared with the CC jacket in relation to the load-carrying capacity. For design purposes, a shear bond stress of 2.96 MPa [0.43 kips per square inch (ksi)] can be used for MMA-PC jackets having an embedment length of at least 127mm (5 in.) whereas a value of 0.83 MPa (0.12 ksi) can be used for CC

Innovative Approach to Repair Corroded Steel Piles using Ultra-High Performance Concrete

Steel H-piles are a common structural system in existing bridges. Many steel H-piles have been corroded as a result of severe weather and acid/alkaline salt exposures, causing a reduction in the axial load capacity. This paper experimentally investigates the use of ultra-high performance concrete (UHPC) encasement as a novel repair method for corroded steel H-pile. UHPC displays better tensile strength, early compressive strength, workability, and durability compared with conventional concrete. The proposed repair is used to bridge the corroded section in H-pile using either a cast-in-place or precast UHPC elements. A series of push-out tests was conducted on eight full-scale piles to assess the axial force that can be transferred through shear studs and bond between the UHPC and steel piles. The test parameters include the type of casting of the UHPC, that is, cast-in-place versus precast elements, thickness and shape of the UHPC elements, an inclusion of carbon fiber reinforced polymer (CFRP) grid, number and grade of bolts, an inclusion of washer, and applying torque on the bolts. The experimental work demonstrated that the UHPC precast repair can be easily implemented. Moreover, using 57mm (2.25 in.) thick UHPC plates reinforced by two layers of the CFRP grid was capable of transferring up to 81% of the squash load of the H-pile

Seismic Performance and Retrofit Evaluation of Hollow-Core Composite Bridge Columns

This paper presents the seismic behavior of large-scale hollow-core fiber-reinforced polymerconcrete-steel (HC-FCS) bridge column. The HC-FCS column consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner thin-walled steel tube. The width-to-diameter ratio for the steel tube was 147. The column had an outer diameter of 24 inches and a height-to-diameter ratio of 4.0. The steel tube was embedded into reinforced concrete footing with an embedded length of 1.25 times the steel tube diameter, while the FRP tube only confined the concrete wall thickness and curtail at the top of the footing level. The column was first tested as a vertical cantilever by applying cyclic horizontal and constant axial loads to the top of the column. Then, the column was repaired using a rapid repair technique within 6 hours duration and retested under the same seismic loading condition. The retrofitting technique includes wrapping three glass FRP layers around the outer bottommost FRP tube that ruptured at the interface joint between the column and the footing during the first test. The results revealed that the HC-FCS column achieved the ductile behavior with good inelastic deformation capacity under seismic loads. While, repaired column performed relatively well under cyclic loading, recovering 34% flexural strength and 80% of the lateral displacement capacity compared to the virgin tested column

Torsional Behavior of Hollow-Core FRP-Concrete-Steel Bridge Columns

This paper presents the behavior of hollow-core fiber reinforced polymer-concrete-steel (HC-FCS) column under pure torsion loading with constant axial load. The HCFCS consists of outer FRP tube and inner steel tube with concrete shell sandwiched between the two tubes. The FRP tube was stopped at the surface of the footing and provided confinement to the concrete shell from outer direction. The steel tube was embedded into the footing to a length of 1.8 times to the diameter of the steel tube. The longitudinal and transversal reinforcements of the column were provided by the steel tube only. A large-scale HC-FCS column with a diameter of 610 mm and height of applied load of 2,438 mm with aspect ratio of 4 was investigated during this study. The study revealed that the torsional behavior of HC-FCS column mainly depended on the stiffness of the steel tube and the interactions among the column components (concrete shell, steel tube, and FRP tube)