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Timber-concrete composite (TCC) connections are crucial elements for transferring loads and dissipating energy for a timber-concrete hybrid system under seismic load. This work investigates the mechanical characteristic of TCC bolted connections and simulates the hysteretic behavior using the simplified models. Specifically, a total of 12 TCC bolted connections were tested subjected to cyclic loading. The variables of bolt diameter, timber thickness and steel pad are investigated. The tested results showed that the connections without steel pads failed with one hinge, whereas those with steel pads failed with two hinges. The steel pad can effectively improve the load-carrying capacity and energy-dissipating capacity. The tested hysteretic curves exhibited strength and stiffness degradation, as well as pinching effect. According to the tested data, the simplified models assigned to two different hysteretic models of Saws and Pinching4 are analyzed and compared. The simulated hysteretic curves from both the Saws and Pinching4 models are consistent with the tested data. The obtained model associated with calibrated parameters is quite useful when such TCC connections are embedded into the analysis of the whole structure.

Timber structures have been a dominant form of construction throughout most of history and continued to serve as a widely used staple of civil infrastructure in the modern era. As a natural material, wood is prone to termite damages, which often cause internal cavities for timber structures. Since internal cavities are invisible and greatly weaken structural load-bearing capacity, an effective method to timber internal cavity detection is of great importance to ensure structural safety. This article proposes an innovative deep neural network (DNN)–based approach for internal cavity detection of timber columns using percussion sound. The influence mechanism of percussion sound with the volume change of internal cavity was studied through theoretical and numerical analysis. A series of percussion tests on timber column specimens with different cavity volumes and environmental variations were conducted to validate the feasibility of the proposed DNN-based approach. Experimental results show high accuracy and generality for cavity severity identification regardless of percussion location, column section shape, and environmental effects, implying great potentials of the proposed approach as a fast tool for determining internal cavity of timber structures in field applications.

Cross-laminated timber (CLT) is a popular construction material that is widely used in timber buildings. In this study, the mechanical properties of three types of CLT connections were investigated: (i) an angle bracket joint; (ii) a crossed self-tapping screw joint; and (iii) a simple butt joint with self-tapping screws. Three repetition tests for each type of CLT connection were conducted under two different cyclic-loading protocols. The experimental results showed that pull-out failure in the tension direction was dominant, whereas wood crushing and screw failure were typical failure modes in the shear direction. An empirical model was used to simulate the nonlinear behavior of the CLT connections under cyclic loading, where the pinching, cyclic stiffness, and strength degradation were considered. To estimate the model parameters associated with the uncertainty of these mechanical properties, the Bayesian approach was proposed, and the Cramer–Rao lower bound was derived as the theoretical lower bound. The parameter-identification results were evaluated according to the elastic stiffness, yielding point, and ductility via equivalent energy elastic–plastic analysis. Comparison of these mechanical properties between the test results and model estimates revealed good agreement. Additionally, the bounds of the estimated response were investigated according to the parameter variance. In comparison with the experimental data, the error bars covered two standard deviations, indicating the reliability of the estimated results. The values of the identified parameters associated with the standard deviation provide a good reference for further analysis when such types of CLT connections are incorporated into a finite-element model of a structural system. The proposed method of Bayesian parameter identification is also suitable for assessing other types of empirical models.

The timber frame is one of the most popular structural systems in the modern timber community. A full-scale test of a timber frame under cyclic loading is executed to investigate the seismic performance. The test results showed that the semirigid joints had a significant influence on the global structural response. Hence, the same type of beam-column joint was also tested to analyze the cyclic behavior. Based on the test results of the full-scale timber frame and beam-column joint, a simplified model whose nonlinearity is assumed to be concentrated plasticity is created. The nonlinear spring element is assigned to the Pinching4 model, where the features of the pinching effect, strength and stiffness degradation are considered. Because the numerical model makes some simplified assumptions that may be different from the actual structural performance, the Bayesian method is employed to update the simplified model using the test data. The statistical characteristics of the updated parameters are estimated from the posterior probability distribution, which can be used for the uncertainty and reliability analysis. The updated model is evaluated in terms of envelope curves, strength degradation and energy dissipation. The comparison results demonstrate that the updated model is accurate and reliable for parametric studies. Furthermore, the influence of gravity loading and various aspect ratios of timber structures on the elastic stiffness and the maximum loading capacity is investigated. The calibrated model of a single timber frame can be easily extended to full-scale and complex structural configurations featuring multiple timber frame structures, providing a reference for timber buildings’ practical design.

The increasing interest in cross-laminated timber (CLT) construction has resulted in multiple international research projects and publications covering the manufacturing and performance of CLT. Multiple regions and countries have adopted provisions for CLT into their engineering design standards and building regulations. Designing and building CLT structures, also in earthquake-prone regions is no longer a domain for early adopters, but is becoming a part of regular timber engineering practice. The increasing interest in CLT construction has resulted in multiple regions and countries adopting provisions for CLT into their engineering design standards. However, given the economic and legal differences between each region, some fundamental issues are treated differently, particularly with respect to seismic design. This article reflects the state-of-the-art on seismic design of CLT buildings including both, the global perspective and regional differences comparing the seismic design practice in Europe, Canada, the United States, New Zealand, Japan, China, and Chile.

Semi-rigidness of the joint connections is one of the main characteristics of timber structures. The pin-joint assumption for the semi-rigid joint connections might be not conservative in the timber structural design. In this paper, structural analysis was conducted on a semi-rigid timber portal frame; the formulas were derived in terms of the internal force and the lateral stiffness, and the influence of the semi-rigid connections was discussed. Moreover, experimental tests were performed on three full-scale timber portal frames and five bolted timber connections to study the lateral performance of the frames and the moment resistance of the connections. For consistency, the connections from the portal frames and the connections for bending tests were of the same configuration. Finally, a calculation flowchart of the lateral performance on a semi-rigid frame was presented to verify the derived formulas and to show a framework of the lateral structural design process.

Composite timber-concrete connections transfer shear forces between the timber component and the concrete through bolts, which improves the effectiveness of the composite action. This paper investigates the influencing factors of timber-concrete connections under shear tests on the loading-carrying capacity, with a specific focus on the effect of steel pads. A series of connections considering the variables of bolt diameters, glulam timber thickness, and the presence or lack of steel pads was tested under monotonic loading. The failure modes of different components are presented and discussed. The mechanical properties extracted from the tested force–displacement curves, including the initial stiffness, yield force, and maximum load-carrying capacity, are analysed and compared. An analytical model considering the effect of steel pads is derived based on the yield theory. The predicted load-carrying capacity of connections using the deriving formulas is consistent with the tested results, which demonstrates that the proposed method is reliable and accurate. The analysis results will provide insight into the mechanical behaviour of timber-concrete connections and guidance for the composite connection design.

A novel wood-concrete system that can be used for high-rise construction in seismically active regions is presented and analysed. The hybrid system is achieved by substituting two out of every three concrete floors and walls in a conventional coupled core wall concrete building with prefabricated light-frame wood modules. To demonstrate the system’s feasibility, a 30-story concrete building and a 30-story hybrid building are designed for the seismicity of Vancouver, Canada, according to the 2015 National Building Code of Canada. Both buildings are evaluated with nonlinear time history analyses. To accurately consider the seismic hazard contribution from the Cascadia subduction zone, a multiple event-based conditional mean spectrum record selection method is adopted to construct target spectra for each hazard source (crustal, subcrustal and subduction). The results show that the seismic mass of the proposed hybrid system is reduced when compared to the concrete building, resulting in a shorter fundamental period but also a lower seismic load demand. The nonlinear time history analyses demonstrated that the hybrid system meets the current seismic code requirements and has lower seismic demands in terms of floor displacement, inter-story drift ratio and story shear forces in both coupling and cantilever directions, demonstrating the feasibility of the proposed system for high-rise construction.

Efforts to increase the use of renewable materials in construction are pushing the use of timber frames into new boundaries—for example, as lateral load-resisting systems in medium to high-rise buildings. This drive brings forth higher performance requirements for timber structures against hazards such as fires and earthquakes. The present study focuses on the development and parameter calibration of a cyclic lateral response model for mass timber frames with knee-braces (MTF-KBs) through a full-scale test. The model primarily comprises plastic hinges, which represent the hysteretic behavior of the MTF-KB specimen. The model parameters are estimated from test data using a Particle Filter (PF) method, which yields the optimal parameters together with their uncertainties. The calibrated model is then used in parametric studies to examine their lateral response, including stiffness and strength degradation, and damage evolution. The performance of MTK-FB in various single- and multi-story structural configurations is also investigated based on this calibrated model, and a novel energy-based damage index is devised that maps visual observations to various thresholds of damage. The proposed MTK-FB model can be readily recalibrated to new/other experimental data. Moreover, the PF-based model updating method presented in this study can be applied to any hysteretic force-displacement data that exhibit complex behavior such as cycle degradation, inelastic deformations, and pinching. The availability of model parameter uncertainties is a useful feature for performance-based seismic assessment studies.

Dowel-type connections are essential components of safe, economical timber buildings. This study analyzes the mechanical properties of different configurations of bolted connections with slotted-in steel plates. The test results indicate that the parallel-to-the-grain connections exhibited three typical failure modes, whereas wood cracking was the predominant failure mode of the connections perpendicular-to-the-grain. The mechanical properties, such as initial stiffness, yielding load, maximum load capacity and ductility, are obtained from load-displacement curves and compared with a design code. The relationship among the mechanical properties, bolt diameter and the thickness of glulam timber is investigated. Based on the experimental load-displacement curves, a two-parameter analytical model related to the initial stiffness and load-carrying capacity is proposed for the prediction of nonlinear load-displacement behavior, and the curves generated using the analytical model are consistent with the test curves. The two physical parameters can also be calculated using the design formulas, rendering the analytical model more useful in practice. This work is beneficial by contributing mechanical knowledge and providing a database for improved connection designs in timber engineering.

Engineered wood-based products manufactured from fast-growing wood species have gained increasing attraction as the demand for using wood in building constructions continues to grow. An innovative oriented oblique strand laminated lumber called Eucalyptus Strand Wood (ESWood) made from fast-growing eucalyptus is presented in this paper. A series of material tests using small clear specimens were carried out to study the basic mechanical properties of the ESWood, while experiments on full-scale columns were conducted to study the buckling behavior of intermediate ESWood columns under centric and eccentric compression. The failure modes and load-carrying capacity of the columns with various eccentricities were reported and evaluated. Efforts were also made to provide a preliminary calculation approach for predicting the critical buckling load of intermediate ESWood columns under both centric and eccentric compression. Based on the analyses presented in this paper, it appears that the oblique strand lamination of ESWood results in great compactness and strength. Compared with the engineered Spruce-pine-fir, wood scrimber, and Glubam, the ESWood has comparable strength to serve as a construction and building material, especially as structural columns. For intermediate ESWood columns under centric and eccentric compression, buckling was observed as the primary failure mode. As the eccentricity increased, the critical buckling load decreased gradually with increasing critical deflection. To predict the inelastic buckling load, Newlin’s formula with either the Newlin-Gahagan approach or Yoshihara approach was adopted. The influence of the yielding stress and critical buckling stress estimation was discussed, and the results show that Newlin’s formula with Yoshihara approach provides good predictions for the critical load of ESWood intermediate columns. The presented test results and analyses provide basic knowledge for supporting more applications of such fast-growing eucalyptus-based material in building constructions.

Connections are important components to cross-laminated timber (CLT) structures. Although there are some hysteretic models available for CLT connections, the main challenge is how to select a predictable and robust model. In this paper, three popular hysteretic models, including the Bilinear model, SAWS model, and Pinching4 model, are briefly revisited. These hysteretic models exhibit their advantages and disadvantages, making them difficult to select the most suitable model for the simulation of hysteretic response. Based on the test data, the Bayesian approach is used to determine the most plausible model from five candidate models. The identified results show that the symmetric Pinching4 model has the highest evidence in shear loading, while in the tension loading the SAWS model possesses the highest value. For the evaluation of the identified results, both the idealized backbone curve and Park-Ang damage index are compared, showing a good agreement between the test and model results. These mechanical characteristics are crucial to the design and rehabilitation of timber buildings.

The Shanghai Tower is presently the tallest structure in China and one of the super tall buildings in the world. To get a quick and direct insight into the overall dynamic behavior of this complex structure, a lumped-mass finite element model based on macro beam theory was developed. Next, an in-depth sensitivity analysis was performed on this baseline model and model updating was conducted by using modal properties obtained from a full-scale field test of this building in its final stage of construction. The difference of the first nine frequencies was reduced from 27% to 4% after updating, and modal assurance criterion value was improved from 73% to 87%. Time history analyses under two severe seismic events were conducted on both the baseline and updated models. The maximum story drift from the updated model were 40% higher than that from the baseline model, demonstrating the significant influence of model updating on its seismic performance. The framework of model updating by simplified updated model for super tall buildings described in this study provides an efficient way to predict their seismic responses, and the outputs are reliable for wide range of applications in the area of long-term heath monitoring and seismic retrofit.

Summary The dynamic characterization of structures is essential for assessing their response when subjected to dynamic loads in structural health monitoring. It mainly comprises the modal parameters, that is, the natural frequencies, damping ratios and mode shapes. These modal properties are attracting more attention when structures are under construction or operation for the researchers, structure owner and engineers. This paper presents the work on the operational modal analysis of a super tall building-the Shanghai Tower with a height of 632 m situated in Shanghai, China. A recently developed fast Bayesian method is utilized to perform modal identification, providing an effective means to identify the modal properties and assess their accuracy. In this study, ambient vibration tests are implemented in different construction stages. The corresponding modal properties and their associated uncertainties are identified and investigated, with interesting trends observed. Finite element models are also established to obtain the modal parameters in different stages and compared with the identified results. After the main structure is completed, a field test covering the eight corners of the core wall in a typical floor is performed to investigate the mode shapes. Afterward, a 12-h measurement is performed with the information of temperature and humidity recorded simultaneously. The variation of modal properties with changing environment is studied. The results obtained will be beneficial for understanding the modal properties of this super tall building and provide a baseline for future structural health monitoring. Copyright © 2016 John Wiley & Sons, Ltd.

In the last few decades structure optimisation has become a main task in a civil engineering project. As a matter of fact, due to the complexity and particularity of every structure, the great amount of variables and design criteria to considerate and many other factors, a general optimisation’s method is not simple to formulate. As a result, this paper focuses on how to provide a successful optimisation method for a particular building type, high-rise reinforced concrete buildings. The optimization method is based on decomposition of the main structure into substructures: floor system, vertical load resisting system, lateral load resisting system and foundation system; then each of the subsystems using the design criteria established at the building codes is improved. Due to the effect of the superstructure optimisation on the foundation system, vertical and lateral load resisting system is the last to be considered after the improvement of floor. Finally, as a case example, using the method explained in the paper, a 30-story-high high-rise residential building complex is analysed and optimised, achieving good results in terms of structural behaviour and diminishing the overall cost of the structure.

The mechanical characteristics of concrete to cross laminated timber (CLT) connections plays an essential role in a hybrid structure. This study mainly deals with an experimental and numerical study on the load-slip behaviour of concrete-CLT connections under cyclic loading, where six specimens with two different loading types (i.e., parallel and perpendicular to the grain of CLT) were executed. The failure modes of all specimens were the bolts shear off at the location of the interface between concrete and CLT, associated with the cracking and splitting of CLT panels depending on loading directions. Then the numerical model whose nonlinearity is concentrated on the spring element is created. To calibrate the model parameters, the procedure of parameter estimation using unscented Kalman filter (UKF) is employed to identify the parameters of a hysteresis model. Two assessment methods, including the equivalent energy elastic-plastic curve assessment and an energy-based damage assessment, are used to comprehensively evaluate the estimated result. The model estimate is consistent with the experimental result, demonstrating the identified parameters having good accuracy. The calibrated parameters of a hysteresis model provide a good database when such type of connections are incorporated into a finite element model of a structural system.

Connections in cross-laminated timber (CLT) structures are crucial components that can affect the behaviour of the whole structure. A novel framework that integrates the unscented Kalman filter (UKF) as an estimation tool with a hysteretic model is developed to identify the model parameters of a nonlinear system. The UKF estimates the mean and covariance of the model parameters using unscented transformation (UT) by a set of deterministically chosen sample points. The proposed framework is applied to identify the unknown model parameters of CLT connections using available experimental data, where the cycle behaviour of CLT connections is simulated using a spring element assigned to the hysteretic model. The comparison of hysteretic curves between the test and model shows that the results identified with UKF are precise. Two different approaches are proposed: an assessment according to the EN 12512 standard, and a damage accumulation assessment. The EN 12512 standard assessment is evaluated from the elastic stiffness, ductility ratio, and energy dissipation, whereas the damage accumulation assessment considers the effects of low amplitude and accumulated damage. Together, these two methods fully evaluate the identified result and the mechanical characteristics of CLT connections. The proposed procedure of parameter identification using the UKF (together with the mechanical properties assessment) can be applied to other connections in timber engineering.

This paper studies the seismic performance of a six-story mid-rise woodframe building under long duration ground motions. The prototype structure was designed by using a performance-based seismic design (PBSD) approach and tested on a shake table at full-scale as part of the NEESWood Project. A three-dimensional finite element model of the structure was developed using the Timber3D program and validated using the shake table test data. Two sets of short and long duration records that had approximately the same response spectra were used for nonlinear dynamic analyses. Fragility curves developed by incremental dynamic analysis (IDA) showed the median collapse capacity of the structure was reduced by 18% for long duration motions compared to the capacity for short duration motions. At the maximum considered earthquake (MCE) intensity level, the estimated median Park and Ang damage index of the structure for long duration motions was increased by 36%.

To study the lateral resistance of bolted glued-laminated (glulam) timber post and beam structures, two monotonic tests and eight cyclic tests were performed on full-scale, one-story, one-bay timber post and beam construction specimens. Four laterally strengthened structural systems were considered: a frame with an X-brace, a frame with a K-brace, a frame with a knee-brace, and a frame filled with light wood shear walls. Seismic performances were evaluated according to the experimental phenomena, hysteretic characteristics, stiffness degradation, strength degradation, and energy dissipation capacity. The results showed that the frame with an X-brace system and the frame with a K-brace system provided markedly better elastic stiffness but lower ductility. The frame with a knee-brace system showed increased elastic stiffness compared with the simple frame system and provided higher ductility compared with both the frame with the X-brace system and the frame with the K-brace system. Additionally, the...

Field tests were conducted on timber floors in three wood-framed buildings in order to obtain their dynamic characteristics and evaluate the vibration comfort. The measured fundamental vibration fr...

Glued-in rod connection for timber structure has shown great potential for engineering applications because of its high strength, stiffness, and aesthetic appeal. During the past few decades, extensive research has been carried out to investigate the effects of geometrical parameters on bonding behavior of glued-in rod connection. On the other hand, comprehensive studies on the effects of material parameters are rare. This article presents an experiment program to study the effects of a number of material parameters—adhesive type, rod surface type, glued-in direction—of glued-in rod connection. Twenty-four glued-in rod specimens were tested using a universal testing machine, and the full bond-slip behaviors of specimens were collected. Test result shows that bond strength of glued-in rod connection with epoxy resin is 20 % to 30 % higher than that with polyurethane, and the effect of rod types on bond strength is negligible. Although parallel-to-grain glued-in rod connection has higher bond strength than that of perpendicular-to-grain connection, sudden brittle failure is observed for parallel-to-grain glued-in rod connection. Furthermore, a new bonding strength model is proposed to account for the effects of material parameters.

This paper presents the detailed experiment setups and data analysis results of the ambient vibration testing of two irregular high-rise buildings done by a joint research team from the University of British Columbia and Tongji University. Two full-scale tests were conducted in May 2015 at the Siping Campus of Tongji University, Shanghai, China. The first Multi-Functional Building (MFB) has 21 stories with a typical floor height of 4 m. The structure shows significant irregularity in both plane and vertical direction, where every three floors combine into one L-shaped unit and the L-shape floor rotates 90° along the height of the building. The second building tested is the Shanghai International Design Center (SIDC). SIDC is an h-shape asymmetry double tower structure consists of main tower (25 story) and secondary tower (12 story). The two towers are rigidly connected with steel truss system between the 11th and 12th floors. Considering the complexities and irregularities of the two buildings, it is essential to study their dynamic properties and the associated principal modes of vibration. Several modal analysis techniques were adopted to determine the modal parameters of two buildings.

The Shanghai Tower is one of the super-tall buildings under construction in the world and will be the tallest structure in China after completion. The building stands approximately 632 m and has 128 stories. It was designed with a double curtain wall system, where a triangular outer facade gradually shrinks and twists clockwise at approximately 120° along the height of the building. On May 8th, 2015, an Ambient Vibration testing was performed on the building in its final stages of construction by a collaborative team from the University of British Columbia and Tongji University. The full-scale test had several purposes that included the evaluation of the current instrumentation techniques and the identification of the dynamic properties of the tower. A set of seven GPS-timed velocity/acceleration recorders was utilized, where two measurements were taken on almost every 15 floors in each setup. This paper presents the signal processing results by using the Frequency Domain Decomposition (FDD) and the Enhanced Frequency Domain Decomposition (EFDD) techniques. The most significant lateral and torsional mode shapes and associated periods of vibration were determined within the frequency range of 0.1–2 Hz. The results will provide useful information for further finite element model update.

Summary The Shanghai Tower is a newly built 127-story and 632 m high super tall building. As of April 2017, it was ranked as the second tallest building in the world. Its main structural system is a mega-frame-tube-outrigger system with six outrigger trusses along the height. Due to its unique structural configuration, a series of field and laboratory model tests have been conducted to better understand its dynamic characteristics. Before its construction, a scaled model of the tower was tested on a shake table, and the results were used to refine the design of the tower. At the completion of the construction, full-scale ambient vibration tests were performed. A Bayesian method was used to perform operational modal analysis from the shake table and full-scale ambient vibration tests. The most probable value of the modal parameters and the associated posterior uncertainties were calculated using this method. The first eight modes were identified, including three translational modes in each principal direction and two torsional modes. Using these results, the dynamic characteristics and associated uncertainties obtained from the two tests were investigated and compared in this paper. Due to the scaling of the model, there are some discrepancies between the natural frequencies obtained from two different tests, but the identified mode shapes matched very well. Although the structure was designed in a very innovative manner, its dynamic characteristics are similar to regular tall buildings. The results from this investigation provide valuable information for an ongoing condition assessment of this super tall building.

The response of low-ductility reinforced concrete (RC) frames, designed typically for a non-seismic region, subjected to two frequencies of base excitations is studied. Five half-scaled, two-bay, two-storey, RC frames, each approximately 5 m wide by 3.3 m high, were subjected to both horizontal and/or vertical base excitations with a frequency of 40 Hz as well as a lower frequency of about 4 Hz (close to the fundamental frequency) using a shake table. The imposed acceleration amplitude ranged from 0.2 to 1.2g. The test results showed that the response characteristics of the structures differed under high- and low-frequency excitations. The frames were able to sustain high-frequency excitations without damage but were inadequate for low-frequency excitations, even though the frames exhibited some ductility. Linear-elastic time-history analysis can predict reasonably well the structural response under high-frequency excitations. As the frames were not designed for seismic loads, the reinforcement detailing may not have been adequate, based on the crack pattern observed. The effect of vertical excitation can cause significant additional forces in the columns and moment reversals in the beams. The ‘strong-column, weak-beam’ approach for lateral load RC frame design is supported by experimental observations. Copyright © 2001 John Wiley & Sons, Ltd.