Study of the fire performance of hybrid steel-timber connections with full-scale tests and finite element modelling

Connection design is critical in timber buildings since the connections tend to have lower strength than the structural members themselves and they tend to fail in a brittle manner. The effect of connection geometry on the fire performance of a hybrid steel-timber shear connection is investigated by full-scale testing. These tests were conducted by exposing the test specimens to the standard time-temperature curve defined by CAN/ULC-S101 (CAN/ULC-S101, 2007)

Seismic response of six-story steel frame building with self-centering energy-dissipative (SCED) braces combined with linear viscous dampers

The self-centering energy-dissipative (SCED) brace is an innovative cross-bracing system that eliminates residual building deformations after seismic events and prevents the progressive drifting that other inelastic systems are prone to experience under long-duration ground motions. Previous studies of SCED braces have focused on the use of friction dampers as the primary energy-dissipating element within the brace. This study uses a six-story prototype building model to determine whether the addition of viscous dampers to the SCED-braced frame can efficiently reduce the accelerations while providing similar or better drift and base shear response. Two main design cases were studied: one with viscous damping only and one where viscous damping was combined with the friction damping within the SCED brace. The viscous damping constant at each story was calculated by determining the equivalent damping necessary to match the energy dissipation provided by a SCED brace with full friction damping at a design drift and modal frequency. The resulting hysteretic behavior of the structure was then modeled using the nonlinear structural analysis package OpenSees to determine the dynamic response of the structures. The best dynamic response was achieved by using 50% of the full SCED brace friction damping combined with viscous damping equivalent to the remaining 50% of the friction damping evaluated at the first modal frequency. This design resulted in a modest 15% increase in base shear while achieving significant performance improvements, decreasing accelerations by 30% and drifts by 20%

Development of a heavy timber moment-resisting frame with ductile steel links

To improve the seismic performance of mid-rise heavy timber moment-resisting frames, a hybrid timbersteel moment-resisting connection was developed that incorporates specially detailed replaceable steel yielding link elements fastened to timber beams and columns using self-tapping screws (STS). Performance of the connection was verified using four 2/3 scale experimental tests. The connection reached a moment of 142 kN?m at the column face while reaching a storey drift angle of 0.05 rad. Two specimens utilizing a dogbone detail in the steel link avoided fracture of the link, while two specimens absent of the dogbone detail underwent brittle failure at 0.05 rad drift. All four test specimens met the acceptance criteria in the AISC 341-10 provisions for steel moment frames. The STS connections exhibited high strength and stiffness, and all timber members and self-tapping screw connections remained elastic. The results of the experimental program indicated that this hybrid connection is capable of achieving a ductility factor similar to that of a steel-only moment-resisting connection. This research suggests that the use of high ductility factors in the design of timber systems that use the proposed hybrid connection would be appropriate, thus lowering seismic design base shears and increasing structure economy

Self-centering energy-dissipative (SCED) Brace: Overview of recent developments and potential applications for tall buildings

The self-centering, energy-dissipative (SCED) brace is an innovative cross-bracing system that eliminates residual building deformations after an earthquake while simultaneously dissipating energy to reduce drifts. Several recent studies are summarized which have confirmed and extended the capabilities of SCE

Adaptation of advanced high R-factor bracing systems into heavy timber frames

Timber provides attractive earthquake performance characteristics for regions of high seismic risk, particularly its high strength-to-weight ratio; however, current timber structural systems are associated with relatively low design force reduction factors due to their low inherent ductility when compared to high-performance concrete and steel systems. This experimental study investigates the adaptation of an advanced structural bracing system for heavy timber frames to improve the seismic performance of hybrid timber-steel buildings. This may justify the use of high force reduction factors (R-factors) to reduce seismic design forces and will provide energy dissipation to improve seismic performance. The study focuses on the design and quasi-static cyclic testing of a friction damping device within a timber frame to dissipate seismic energy and increase seismic performance. The bracing system is incorporated into the timber frame using select steel elements at the beam-column connections and glued-in rods to fasten the steel and timber elements together. The test frame demonstrated excellent cyclic performance, high ductility and did not experience any damage in timber connections, supporting the use of this type of connection detail in heavy timber structures

Nailed connection behavior in light-frame wood shear walls with an intermediate layer of insulation

The shear strength and stiffness of light-frame wood shear walls is highly dependent on the behavior of their individual nailed connections. Eighty-four nailed connection specimens were tested under shear loading to determine the effect of including rigid insulation as an intermediate material between the sheathing and framing elements in a light-frame wood shear wall. Each specimen contained common 10d or 16d nails, 15.9 mm oriented strandboard sheathing, spruce-pine-fir lumber, and rigid insulation in varied thicknesses between 0 and 38.1 mm. From the load-deformation results, maximum load, yield load, and stiffness were assessed using curve-fitting and yield-point determination methods. The results indicate that, as the insulation thickness increases, the connection strength and stiffness both exhibit a steep reduction. In addition, nonlinear two-dimensional (2D) finite-element models of the same nailed connections were developed. These models showed good correlation with experimental data and served to confirm that the decline in strength and stiffness observed in the tests is due to the introduction of the insulation

Development and testing of hybrid timber-steel braced frames

The practical use of high-performance structural steel bracing systems in heavy timber buildings has not previously been explored. This study investigates the design and behavior of a prototype steel beam to column bracing connection to enable the use of friction damping devices, buckling restrained braces (BRBs) and other high-performance braces to create hybrid timber-steel braced frames. Glued-in rods, with and without pre-tensioning, are used to connect the steel and timber elements in the frame. The timber elements and connections are designed to remain elastic using capacity design principles, allowing the frame to behave similarly to comparable steel high-performance braced frames. A test frame incorporating the new hybrid beam to column bracing connection system with a friction brace device was evaluated and validated using a half scale test of a beam-column-brace connection under wind loading and BRB qualification protocol loading. The tests showed that the connections and timber members remained elastic and could accommodate at least two times the design drift at full load. They also showed that pre-tensioning the glued-in rod connections did not affect the global system performance

Testing and analytical modelling of intermediate gypsum wallboard in wood shear wall sheathing to framing connections

Light frame wood shear walls resist lateral loads primarily through the individual nailed connections between the sheathing and framing. The most common arrangement for such shear walls is to have sheathing on one side and gypsum board on the other. In various situations it can be desirable to increase the capacity of this type of walls by fastening a layer of sheathing overtop of the drywall. This study considered the effect that an intermediate layer of gypsum has on the strength of nailed connections in shear walls, while maintaining code-defined minimum nail penetrations. Results show that intermediate gypsum placed between the sheathing and framing resulted in significantly reduced capacity and stiffness. Analytical modelling showed good correlation with experimental results. The implications of the experimental testing and modelling are that code provisions allowing the use of intermediate gypsum wallboard should not be relied upon

Design, Testing, and Detailed Component Modeling of a High-Capacity Self-Centering Energy-Dissipative Brace

The self-centering energy-dissipative (SCED) brace is an innovative cross brace for buildings that provides a nonlinear response with good energy dissipation and postyield stiffness while minimizing residual drift after an earthquake. This provides a high level of seismic performance by allowing structures to remain operational even after major seismic events. Recently, the SCED brace has been improved through the design and experimental evaluation of a high-capacity SCED (HC-SCED) that has an axial capacity similar to some of the largest available conventional cross braces for buildings. This prototype HC-SCED satisfied testing protocols for buckling-restrained braces and exhibited full self-centering behavior during cycles up to 1.5% drift. To characterize the hysteretic response of the brace in detail, a new analytical approach is developed. This new approach is necessary because simplified stiffness estimates do not provide good predictions of the low-amplitude displacement response and initial effective stiffness that was measured in the full-scale experiments. The proposed analytical approach includes the effects of fabrication tolerances, which have been identified as the main reason for incorrect low-amplitude displacement predictions that result from the simplified stiffness estimates. Using the results from the HC-SCED tests, the new analytical approach provided good estimates of the initial stiffness of the braces and also was able to predict the behavior of the brace well under a larger fabrication tolerance scenario. These improved predictions may be used to improve the characterization of the effective hysteretic behavior of actual SCED braces for use in nonlinear time history analyses

Detailed component modelling of a self-centering energy dissipative brace system

The self-centering energy-dissipative (SCED) brace is a new steel bracing member that provides damping to a structure and a re-centering capability, reducing or eliminating residual building deformations after major seismic events. Recently, the SCED concept has been extended through the design and construction of a new enhanced-elongation telescoping SCED (or T-SCED) brace that allows for self-centering behaviour over a range that is two times as large as the range that could be achieved by the original SCED bracing system. Previous prototype tests of SCED and T-SCED braces have shown that the simplified estimates of the initial brace stiffness that were previously used do not predict the results from the prototype tests well. To accurately model the mechanics of these new systems, a new software tool has been developed that is able to represent the detailed behaviour of SCED braces to determine realistic brace stiffness and the effect of construction tolerances on the br