Xiaobin Song

Mechanical Behavior of FRP-Strengthened Concrete Columns Subjected to Concentric and Eccentric Compression Loading

This paper presents the results of a study on the mechanical behavior of concrete columns strengthened with fiber-reinforced polymer (FRP) and subjected to concentric and eccentric compression loading. A numerical analysis model was developed based on the effectively confined concrete area and the stress-strain relationship of the confined concrete established based on compression tests of circular plain concrete columns. The model was verified against the test results of square concentrically loaded plain concrete columns and square eccentrically loaded reinforced concrete columns. An analytical formula of the maximum compression load of square or rectangular fiber reinforced polymer strengthened concrete columns, with respect to the same but nonstrengthened columns, was developed based on the parametric study results by using the verified model. The analytical formula was further verified with the test results of 23 square and rectangular fiber reinforced polymer strengthened columns reported in the literature. Good agreement was achieved. It was found that the increase of the maximum compression load of FRP-strengthened concrete columns, with respect to the same but nonstrengthened columns, increases linearly with the amount of FRP sheets used and decreases linearly with the load eccentricity and exponentially with the concrete compression strength. The last observation implies that the FRP strengthening technique (through wrapping) is most suitable for low-strength concrete buildings.

Compressive Behavior of Longitudinally Cracked Timber Columns Retrofitted Using FRP Sheets

This paper presents the results of a study on the compressive behavior of timber columns with longitudinal cracks. Material property tests and full-scale compression tests were conducted to investigate the failure modes and the recovery in the load-carrying capacity of cracked timber columns with the use of fiber-reinforced polymer (FRP) sheet wrapping. Different combinations of column geometries, crack dimensions, and types and spacing of FRP sheets were considered. A finite-element method (FEM)-based model was developed and verified on the basis of the test results. A parametric study was also conducted by using the verified model to further quantify the influences of crack dimensions and types and spacing of the FRP sheets. It was found that wrapping FRP sheets around cracked timber columns can recover their load-carrying capacity by up to 20%.

Rotational Behavior of Bolted Beam-to-Column Connections with Locally Cross-Laminated Glulam

This paper summarizes the results of an experimental study on the rotational behavior of bolted beam-to-column glulam connections reinforced using locally cross-laminated glulam members. Twenty-two full-scale connection specimens were tested through monotonic and reversed cyclic loading, from which the moment / rotational angle relationships were established. The results indicated that the cross-laminated technique leads to a more ductile failure mode with cross-aligned inner layers of laminas fractured, in contrast to the perpendicular-to-wood-grain tensile failure of unreinforced connections. The connection maximum moment was found to increase by 52% and 46% under monotonic and cyclic loading, respectively; moreover, the deformability ratio evaluated on the basis of the rotation angles corresponding to the yielding and maximum moments of the connections was increased by 94%. Locally cross-laminated connections were also found to dissipate more energy (25%) than unreinforced connections. A comparison of the cross-laminated technique with self-tapping screws indicated that the respective reinforcing effects were comparable with that of the screws being slightly higher. Because the locally cross-laminated technique is readily incorporated into the production of cross-laminated timber products, it may have broad applications in heavy timber-bolted connections.

Stability Capacity and Lateral Bracing Requirements of Wood Beam-Columns

This paper presents a study on the stability capacity and lateral bracing requirements of wood beam-columns subjected to biaxial eccentric compression loads. Material property tests and wood beam-column tests were conducted to provide input parameters and verification to a finite element method based numerical analysis model. The model provided good predictions of the maximum compression load, midspan lateral deflection and lateral bracing force of the wood beam-columns. A parametric study was conducted for the effect of the lateral bracing stiffness, load eccentricity and initial lateral deflections. The adequacy of the 2% rule-of-thumb, Winters and Plauts methods was also studied by comparing to the test results of the lateral bracing force. The developed model and its output can be used to improve the design methods of the lateral bracing systems of wood beam-columns.

Stability Analysis of Metal-Plate-Connected Wood Truss Assemblies

AbstractThis paper presents a study on the critical buckling load and lateral bracing force of metal-plate-connected (MPC) wood truss assemblies. A three-dimensional finite-element method (FEM) based computer program was developed, calibrated, and verified with test results. A preliminary reliability analysis was conducted based on the verified FEM model, with consideration of the variation in material properties and the initial out-of-plane deflection of compression webs. The out-of-plane rotational stiffness of MPC connections has a significant effect on the critical buckling load and lateral bracing force ratio of MPC trusses. The critical buckling load could almost be doubled on the basis of an ideally pinned compression web, and the lateral bracing force ratio was found to be generally less than 1% from the test results and numerical analysis. Consequently, the currently used 2% rule of thumb for lateral bracing design may be conservative, by overestimating the lateral bracing force, and may lead to ...

Stability Capacity of Metal Plate Connected Wood Truss Assemblies

This paper presents the results of an experimental study on the critical buckling load and lateral bracing force of metal plate connected wood truss assemblies. Material property tests—including the modulus of elasticity of dimension lumber, flexural stiffness of plywood panels, and load-slip relationship of nail connection—and full-scale tests of individual trusses and truss assemblies were conducted. The critical buckling load and lateral bracing force were recorded. The continuous lateral bracing, the load sharing and distribution effects, and the residual deformation at the metal plate connections were studied for their influence on the system’s stability performance. The adequacy of the 2% rule of thumb, which is used by some design engineers for lateral bracing system design, was also discussed by comparing to the test results of the lateral bracing forces. The generated database can be used as input parameters and for verification for numerical analysis models and therefore contributes to the impro...

Compressive Stress Strain Relationship of Wood Confined with Fiber Composite Sheets

This paper presents the results of an experimental study on the compressive stress-strain relationship of wood confined with fiber composite sheets. Wood cylinders confined with carbon fiber composite sheets along full length were tested by compression load. The tests considered up to three layers of fiber sheets. The results will be used to verify a numerical analysis model, which will be further used to conduct a parametric study of the influential factors. The generated knowledge can be used as reference for strengthening designs of historical timber structures using fiber reinforcing products.

New Method for Surveying and Mapping Architectural Plane In-House with Laser Reticule Images

Surveying and mapping the appearance of architecture plane is a supporting technology of historic buildings. To meet the need of plan survey in-house, a new close-range photogrammetry method was developed by laser reticule system. With the help of the system, two parallel level lines and eight vertical laser lines can be marked on the surface of inner walls. When the relationship between the distance from a vertical line and the length of the same line on an image picture is studied, the spatial location of room corners and some characteristic points on the images can be determined. Based on the photogrammetry and plane table operation method, architectural plane mapping can be done easily following a set of laser reticule images which were shot in situ closed by a non-metric digital camera. More details of historic buildings can be recorded on drawing sheets and images monogamy at the same time by using the proposed method, which are the basic information for the structural analysis of historic buildings.

Stability Analysis of Eccentrically Loaded Wood Beam-Columns

Wood beam-columns are mostly subjected to three-dimensional load effects, such as combined compressive load and biaxial bending moment. Without appropriate provision of lateral bracings, they are susceptible to buckling in weak axis. Many research activities have been conducted to investigate the stability capacity of wood beam-columns under eccentric compression load. However, most of these research were restricted to two-dimensional problems due to the modeling or experimental difficulties. Song presented a numerical analysis procedure based on Column Deflection Curve (CDC) method and considered the biaxial bending moment. However, the CDC method can not trace the post-buckling behavior. This paper presents a Finite Element Method (FEM) based three-dimensional analysis to study the stability capacity of wood beam column subjected to compressive load and biaxial bending moments. The model considers the material nonlinearity, geometrical changes and variation of wood mechanical properties applicable to wood beam-columns with various boundary conditions. The Arc-length and Newton Raphson methods are incorporated to trace the post-buckling behavior. Parallel-to-grain wood compression and tension test and biaxial eccentric compression test of wood beam-columns were conducted to provide input data and verification for the FEM model from the perspective of stability performance.

Carbon Fiber–Reinforced Polymer Reinforcement for Rotational Behavior of Bolted Glulam Beam-to-Column Connections

AbstractThis paper presents the results of an experimental study on the use of carbon fiber–reinforced polymer sheets as reinforcement for the rotational behavior of bolted glulam beam-to-column connections. Monotonic loading was applied on connection specimens to identify their stiffness, ductility, and maximum moment resistance values. Material property tests were conducted and used to provide an unbiased judgment of the reinforcing efficiency considering varied specimen qualities. Different sheet wrapping patterns and layers of sheets were examined, and the results were compared with each other and results from previous studies. It was found that carbon fiber–reinforced polymer sheets could improve the moment capacity of unreinforced connections by up to 59%, which is very close to the reinforcing ratio (65%) achieved by using locally cross-laminated glulam members. A linear relationship was found between the increased perpendicular-to-grain glulam tensile strength and the increased moment resistance b...