Frank Lam

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Performance of strand-based wood composite post-and-beam shear wall system (2016)

This dissertation proposes a strand-based wood composite product to be utilized as the vertical members of post-and-beam (P&B) shear walls. Since the shear wall performance is largely governed by connection systems holding the wall components together, the research focuses on the structural behaviour of two key connection types: nail and hold-down connections. The experimental studies were designed to evaluate the effects of orthogonal properties, such as vertical density profile of the strand-based product, on the connection performance. Static load tests were conducted following ASTM standards and Japanese HOWTEC connection performance guidelines. The test results showed that the connections with fasteners mounted on the face-side of the composite product outperform the ones with fasteners mounted on the product’s edge-side. Subsequently, full-scale shear wall tests were conducted on three P&B wall types to study the effect of the fastener driving direction on the wall performance. The test results confirmed that the shear walls with face-driven nails outperforms the ones with edge-driven nails in terms of load carrying capacity.A detailed mechanics-based finite-element connection model RHYST was also developed to predict the load-displacement relationship of a nail connection. It was developed based on an existing connection model HYST which idealizes a dowel-type connector driven into a wood medium as an elasto-plastic beam embedded in a nonlinear foundation that only acts in compression. RHYST assumes that the lateral response of the wood medium does not decrease at any compressive displacement. The presented model takes into account the contribution of the fastener’s vertical displacements on the response of the foundation. The simulation results of RHYST agreed well with the reversed-cyclic nail connection test results in terms of load carrying capacity and energy dissipation. The model is also able to simulate strength and stiffness degradation between the repeated loading cycles. Moreover, the applicability of RHYST was confirmed by incorporating it as a subroutine in a finite-element shear wall model WALL2D. The simulation results of WALL2D with RHYST showed a good agreement with the wall test results.

View record

Duration-of-load and size effects on the rolling shear strength of cross laminated timber (2015)

In the beginning of the twenty-first century, the largest mountain pine beetle (MPB) outbreak ever recorded struck western Canada. A huge volume of MPB-attacked lodgepole pine is expected to hit the BC forest industry in the next decade. Technologies to convert MPB-attacked lumber into engineering wood products are urgently required. Cross laminated timber (CLT) is a technology that can produce massive timber members as an engineered wood product for timber structures.In this study, the duration-of-load and size effects on the rolling shear strength of CLT manufactured from MPB-afflicted lumber were evaluated. The study of the duration-of-load effect on the strength properties of wood products is typically challenging; and, additional complexity exists with the duration-of-load effect on the rolling shear strength of CLT, given the necessary consideration of crosswise layups of wood boards, existing gaps and glue bonding between layers.In this research, short-term ramp loading tests and long-term trapezoidal fatigue loading tests (damage accumulation tests) were used to study the duration-of-load behaviour of the rolling shear strength of CLT. In the ramp loading test, three-layer CLT products showed a relatively lower rolling shear load-carrying capacity. Torque loading tests on CLT tubes were also performed. The finite element method was adopted to simulate the structural behaviour of CLT specimens. Evaluation of the rolling shear strength based on test data was discussed. The size effect on the rolling shear strength was investigated.A stress-based damage accumulation theory was used to evaluate the duration-of-load effect on CLT rolling shear. The model was first calibrated against the test data and used to investigate the long-term CLT rolling shear strength. A reliability-based method was then applied to assess the CLT rolling shear performance. Finally, a duration-of-load adjustment factor for CLT rolling shear strength was established. The duration-of-load adjustment factor for the three-layer and five-layer CLT is different from that for lumber. The results suggest that the rolling shear duration-of-load strength adjustment factor for CLT is more severe than the general duration-of-load adjustment factor for lumber, and this difference should be considered in the introduction of CLT into the building codes for engineered wood design.

View record

Three-dimensional modeling of metal plate connected wood truss joints (2013)

This thesis presents theoretical and experimental studies of metal-plate-connected (MPC) wood truss joints under uni-directional tension or out-of-plane bending. A theoretical computer program, SAMPC, was developed based on finite element method (FEM). MPC joint models were constructed using SAMPC, to evaluate the three-dimensional nonlinear performance of the joints.Experimental studies were carried out on MPC truss joints under tension. The joint failure modes were discussed, and the potential reasons for the failure were explored. Data processing techniques were applied to obtain the specific load-displacement relationships, which were in turn used as reference for model calibration and verification. Based on the experimental results, optimized model parameter calibration and model verification were discussed. The program application of MPC joints subjected to out-of-plane bending was investigated. Comparisons of the results from the joint bending test and model verified the applicability of the program for evaluating the out-of-plane rotational stiffness of MPC joints.A reliability analysis was conducted to evaluate the critical buckling load and lateral bracing force of single- and double-braced wood truss web systems. The probability characteristics of a number of variables that affect the performance of braced truss web system were investigated. Based on the results, a factor relating the ratio of the lateral restraining force and axial load was established. This factor with adequate reliability was recommended as a web/bracing design amendment to Canadian Code on Engineering Design of Wood.For the investigated truss joints, SAMPC appears to be superior in terms of its ability to simulate MPC joints in elaborate detail. This detailed model can aid in developing a better understanding of joint behavior under realistic joint configurations and loading conditions. The ability of the model to accurately predict the behavior of the designed MPC joints brings up the potential of modeling joints composed of different wood species and truss plate types featuring more complex joint configurations and loading conditions. The body of information from modeling results can be used to evaluate the adequacy of a given structural design, to facilitate truss plate, truss joint and overall truss design.

View record

Creep behaviour of wood-plastic composites (2011)

In this research, a series of experiments have been conducted, including mountain pine beetle attacked wood/plastic composite (MPB-WPC) prototype product development, dynamic mechanical analysis (DMA), short-term creep tests for master curve construction based on the time-temperature-stress superposition principle (TTSSP), and a long-term creep test. Moreover, a newly established stress-temperature incorporated creep (STIC) model, a modified Williams-Landel-Ferry (WLF) equation that incorporates the variables of temperature and stress, and a newly developed temperature-induced strain superposition (TISS) method were introduced.The MPB-WPC products showed definite potential as a value-added product option for MPB-attacked wood. The formulation affected the MPB-WPC products’ properties. The capacity of the products without a coupling agent was considerably inferior to the product formulations that included a coupling agent. The surface condition of the product was also influenced by the formulation. The dynamic mechanical properties were studied. The mechanical and viscoelastic behaviours of the MPB-WPC products were considerably influenced by the formulation of wood and plastic and the presence of a coupling agent, which can be attributed to modification of the interface property and the internal structure.The new STIC model smoothly introduced the effect of temperature into a conventional power law creep equation, and the model can be applied to predict the creep strain in which the effect of temperature is involved. Moreover, the temperature-stress hybrid shift factor and a modified WLF equation were studied; and, the parameters were successfully calibrated.Temperature-induced strain was observed in the results of the 220-day creep test. For a temperature-sensitive material like WPCs, the information obtained from conventional creep studies is not sufficient to predict long-term performance. The comparison between the long-term creep data and the master curves showed that master curves tended to overestimate the creep strain. Generally, the master curves constructed based on TTSSP cannot precisely predict the long-term creep strain, but can provide conservative estimations. To deal with the effect of fluctuating temperatures on the creep strain, the STIC model and the proposed temperature-induced strain superposition (TISS) method were established and employed. The additional temperature-induced creep strain and overall behaviour were successfully simulated.

View record

Structural performance of box based cross laminated timber system used in floor applications (2011)

The current outbreak of Mountain Pine Beetle (MPB) in the province of British Columbia (B.C.) is the most extensive disturbance event occurring in North American forests in recorded history. The concept of converting the beetle killed wood into engineered wood products by defect removal and reconstitution is employed to maximize value recovery from the material. Cross Laminated Timber (CLT), which is produced in modular form and can be utilized as part of a structural system for floor, wall or roof elements, is considered as an excellent application of the concept. CLT originates from Europe. Such products have been developed as a proprietary product by individual companies aimed at servicing specific markets. There is a need to investigate different ways of making CLT and to define its structural performance suitable for North America. The main focus of this study is to investigate the structural performance of box based CLT system used in floor applications. Comprehensive three dimensional finite element models, which can be used to analyze the mechanical and vibration behavior of the plate and box type structures, were developed. Four prototype box elements, each having five replicates, were designed and manufactured locally. Third point bending tests were conducted on the specimens in the Timber Engineering and Applied Mechanics (TEAM) Laboratory at the University of British Columbia. The numerical analysis agreed well with experimental data in terms of vertical deflection and bending stiffness. Vibration, which is critical to floor serviceability, was also studied. Three types of excitation were applied to measure the fundamental frequency of the twenty specimens. Finite element analysis provided good predictions of fundamental frequency values comparing to the experimental results. A local built demonstration building, L41home, was presented and analyzed as an example using the tools developed in this study for CLT applications. As a pioneer research of CLT materials in North America, this work has contributed to the understanding of the structural performance of floor systems using CLT panels for the commercial and residential applications.

View record

Duration-of-load and creep effects in thick MPB strand based wood composite (2010)

British Columbia (BC) is in the midst of the largest outbreak of the Mountain Pine Beetle (MPB) ever recorded in western Canada. Technologies capable of converting stained lumber into market acceptable products are urgently required to reduce the impact of the growing volume of MPB killed lumber on the profitability of forestry in BC.New, thick MPB strand-based structural composite products can be produced and help absorb a large volume of MPB wood. With appropriate mechanical properties, such products can be used as beams, headers, and columns in the low-rise commercial, multi-family residential and single family residential markets.This work was focused on the duration-load and creep behaviour of thick MPB strand-based wood composite. The beam specimens were made in the Timber Engineering and Applied Mechanics Laboratory at UBC. A series of tests were conducted on the matched groups to investigate the creep-rupture behaviour. These investigations comprised of ramp load tests at three loading rates, long-term constant load tests at two stress levels and cyclic bending tests at six stress levels. A damage accumulation model was developed to study the creep-rupture behaviour. This model stipulates that the rate of damage growth is given in terms of the current strain rate and the previously accumulated damage, and a 5-parameter rheological model is applied to describe the viscoelastic constitutive relationship to represent the time-dependent strain, while the damage accumulation law acts as the failure criterion. The results of the long-term constant load tests were then interpreted by means of the creep-rupture model which had been shown to be able to represent the time-dependent deflection and time-to-failure data for different stress levels. The predictions of the model were verified using results from ramp load tests at different loading rates and results from cyclic loading tests at different stress levels. The creep-rupture model incorporates the short term strength of the material, the load history and predicts the deflection history as well as the time-to-failure. As it is a probabilistic model, it allows its incorporation into a time-reliability study of wood composites’ applications.

View record

Seismic performance of post-and-beam wood buildings (2009)

This thesis presents a study to evaluate the seismic performance of post-and-beam(P&B) wood assemblies and buildings of Japanese style using computer modeling,experimental studies and probabilistic-based approaches.A numerical model called “PB3D” is proposed to predict the lateral response of theP&B buildings under static or dynamic loads. Special techniques are used to reduce theproblem size and improve computational efficiency with reasonable prediction accuracy.This model simplifies a P&B building into a combination of 2D assemblies (e.g. shearwalls, floor/roof diaphragms) while capturing the global structural responses of interest(e.g., inter-story drift and floor/roof acceleration). A mechanics-based wood shear wallmodel is implemented to represent the hysteretic properties of symmetric/nonsymmetricP&B walls. Roof/floor diaphragms are modeled as structural frames with calibratedequivalent diagonal braces in order to consider the influence of the diaphragm in-planestiffness on the building performance.Experimental studies have been conducted to study the behavior of 2D assembliesand buildings. The engineering characteristics of single-brace P&B walls have beenevaluated by monotonic and reversed cyclic tests. The contribution of additional gypsumwallboards to the wall lateral resistance has also been studied. An in-plane pushover testhas been conducted to study the in-plane stiffness of a floor diaphragm. Two one-storyP&B buildings have been tested under biaxial static loads and one-directional seismic loads, respectively. The established test database as well as a test database of a two-storyP&B building provided by a research institute in Japan has been used to verify the “PB3D”model.Using the response surface method with importance sampling and considering theuncertainties involved in seismic ground motions, structural mass, and response surfacefitting errors, seismic reliability analyses have been conducted to estimate the seismicreliabilities of a series of shear walls, a one-story building and a two-story building.System effect on the shear wall reliability has also been studied.The framework presented in this thesis provides a useful tool to assess the seismicperformance of the P&B wood buildings and to aid the performance-based seismic designof these structural systems.

View record

Stability and reliability analysis of metal plate connected wood truss assemblies (2009)

This thesis describes a study on the stability capacity and lateral bracing force of woodbeam-columns and metal plate connected (MPC) wood truss assemblies.A user-friendly computer program, SATA, was developed based on the finite elementmethod (FEM). The program can be used to perform three-dimensional nonlinear structuralanalyses by using the Newton-Raphson and arc-length methods. The Monte Carlo simulationand response surface methods have also been incorporated into the program for the purpose ofreliability analyses.Experimental studies were conducted to provide input parameters and verification forthe developed software. Material property tests were performed to consider a variety ofmaterials. Biaxial eccentric compression tests of wood beam-columns and full-scale tests ofMPC wood truss assemblies were also carried out to study the critical buckling load and lateralbracing force. The program predictions were in good agreement with the test results.A reliability analysis was conducted for a simplified MPC wood truss assembly usingthe developed program. The effect of the variation of the structural behaviour and externalloads on the critical buckling load of the truss assembly was studied. The adequacy of the 2%rule-of-thumb was also studied.This research bridges the knowledge gap that currently exists in the understanding anddesign of MPC wood truss assemblies and their lateral bracing systems. The test database andthe output of the developed program contributes to the development of more efficient designmethods for MPC wood truss assemblies and other structures where buckling failure is ofconcern.

View record

Master's Student Supervision (2010 - 2018)
Failure mechanism of rolling shear failure in cross-laminated timber (2016)

Wood as building material is gaining more and more attention in the 21st century due to its positive attributes such as light weight, renewability, low carbon footprint and fast construction period. Cross-laminated timber (CLT), as one of the new engineered wood products, requires more research emphasis since its mechanical performance can allow CLT to be utilized in massive timber structures. This thesis focuses on revealing one of the key failure mechanisms of CLT, which is usually referred to as the rolling shear failure. The scientific research conducted in this thesis combined both analytical modelling and experimental material testing. The stresses in CLT cross-layers obtained from a finite-element model were analyzed to differentiate various failure modes possible. Tension perpendicular to grain stress was found to cause cross-layer failure in combined with the rolling shear stress. Experimentally, specimens prepared from 5-layer CLT panels were tested under center-point bending condition. Detailed failure mechanism of CLT cross-layers were recorded with high speed camera to capture the instant when initial failure happened. It is evident that some of the specimens failed in tension perpendicular to grain which verified the modelling results. Variables such as the rate of loading and the manufacturing clamping pressure were designed in experiments to compare their influence to the failure of CLT specimens. In this research, the failure of CLT cross-layer was updated to a combined consequence of both rolling shear stress and tension perpendicular to grain stress. Future research topics and product improvement potentials were given by the end of this thesis.

View record

Numerical study of pin-supported cross-laminated timber (CLT) shear wall system equipped with low-yield steel dampers (2016)

This thesis presents a numerical study of a novel rocking cross-laminated timber (CLT) shear wall system for low- to mid-rise constructions. The system takes advantage of the high in-plane stiffness of CLT coupled with low-yield steel dampers to control the rocking motion of the CLT shear walls during earthquakes. The low-yield steel dampers connected between two rigid CLT wall panels provide the mechanism needed to dissipate the earthquake energy. This concentrates the damage in the dampers, allowing the system to be repaired efficiently after major earthquakes. Numerical models of the CLT shear wall system have been developed using both OpenSees Navigator and ABAQUS software. Models of low-yield steel damper systems were calibrated using available experimental results. With the rigid floor/roof assumption, a simplified OpenSees model of the CLT shear wall system was demonstrated to be effective and reasonably accurate in predicting the response of the system under large excitations. Therefore, it is efficient and reliable to apply the OpenSees model to study the seismic response of CLT shear wall buildings. A case study of a six-storey CLT shear wall building located in Vancouver, Canada was studied; and, detailed parameteric studies were conducted to investigate the influences of the damper type (damper shear strength), number of dampers, damper location, different earthquake records versus target earthquake design response spectrum, and earthquake peak ground acceleration (PGA) on the building response. It was determined that an optimized damper design with comprehensive consideration of these five factors can provide a building with a small roof drift ratio, as well as minor damages on the dampers. Concepts and examples for connection design are also provided.

View record

Self-tapping screw assemblies under monotonic and reverse cyclic load (2012)

In the past century old-growth forests in Canada and the USA provided sufficiently large, clear wooden construction material which have been extensively used. Today, the importance of high-quality structural timber and wood products has increased by far. This increase in demand for high-quality timber and wood products can only be satisfied with second-growth wood, some remaining old-growth forests, and of course engineered wood products. The performance of these materials in structures is, however, largely influenced by the capacity of connections. The envelope in timber construction can only be pushed forward if research on mechanical fasteners and connections that are strong, reliable and cost efficient is conducted. Primary focus of research must address the inherent tensile and shear weaknesses of wood perpendicular and parallel to the wood grain.The thesis presented here experimentally investigates the performance of newly evolved structural self-tapping full thread wood screws as a primary fastener in Canadian Douglas-fir glulam and Cross-Laminated-Timber. The screws as primary fasteners were investigated in a commonly used shear connection and a recently developed moment resisting assembly under reverse cyclic load. Both connection systems utilize the high withdrawal resistance and tensile strength of the fastener with inclined (screw-in angles between 30° and 45°) arrangements. The inclined arrangement allows force transfer along the fastener axis and therefore reduces perpendicular to grain splitting and parallel to grain shear failure and provides high connection capacities and stiffness. The results show that structural self-tapping wood screws can effectively be used as primary connector under reverse cyclic loading conditions. In addition to the screw’s superior withdrawal resistance and tensile strength the research showed that self-tapping screws can be applied efficiently with commonly available machinery and tools.

View record

A comparative life cycle assessment of mid-rise office building construction alternatives : laminated timber or reinforced concrete (2011)

The objective of this project aimed to quantify and compare the environmental impacts associated with the construction of a mid-rise office building. Two alternative scenarios were considered; a traditional cast-in-place, reinforced concrete frame and a laminated timber hybrid design, which utilized engineered wood products including glulam and cross-laminated timber (CLT). The study boundary was cradle-to-gate and encompassed the structural support system and the building enclosure.A case study building; Discovery Place – Building 12, was selected to represent a typical five-storey office building constructed in North America. Floor plans, elevations, material quantities and design loads associated with the concrete-framed building design were obtained from issued-for-construction engineering drawings. A functionally equivalent, laminated timber design was then conceived, based on the requirements outlined in CAN/CSA-O86-01. Design values for locally produced CLT panels were established from in-house material testing results. A life cycle assessment of CLT, manufactured in British Columbia with mountain pine beetle killed wood, was developed based on primary inventory data collected from a pilot-scale manufacturing facility. Life cycle inventory and impact assessment data for building materials was obtained from secondary sources including BEES® 4.0, ATHENA® EcoCalculator, CORRIM, and the US LCI. TRACI, an impact assessment characterization methodology, was employed to translate inventory flows into environmental impact indicators. The environmental comparison of building design alternatives was based on 11 impact categories. The results concluded that the laminated timber building design was associated with a lower environmental footprint in 10 of 11 categories. At a minimum, the heavy timber design demonstrated a 14% improvement, when considering acidification potential. At a maximum, the timber design exhibited a global warming potential that was 71% less than the concrete design. Fossil fuel depletion was the only category where the concrete design was superior, displaying a 6% advantage over the timber scenario. The cumulative embodied energy of construction materials was also calculated; with results estimating energy contents of 116 and 66 terajoules for the timber and concrete designs, respectively. The concrete building acquired 20% of its energy from renewable sources, whereas in the timber-framed case, renewables accounted for over 60% of the combined feedstock and process energy.

View record

Social encounters in daily life and two-year changes in metabolic risk factors in young women (2011)

Research shows that poor social ties increase risks of morbidity and mortality from cardiovascular disease (CVD). However, little is known about the nature of everyday social encounters that give rise to this association, or when in the course of development they begin to shape disease-relevant biological processes. In this study, 122 adolescent females recorded the qualities of their everyday social interactions using electronic diaries. At the same time we measured components of the metabolic syndrome, a precursor to CVD that includes central adiposity, high blood pressure, insulin resistance, and lipid dysregulation. Metabolic symptoms were reassessed 12 and 24 months later. Hierarchical linear modeling revealed an association between negative social interactions and metabolic symptom trajectories. To the extent that participants had more intense negative social encounters in daily life, they showed increasing scores on a composite indicator of metabolic risk over two years. This association was independent of a variety of potential confounders, and persisted when symptoms of depression and broader personality traits were controlled. There was no association between positive social encounters and metabolic risk trajectories. These findings suggest that even in otherwise healthy adolescents, abrasive social encounters may accelerate the progression of CVD’s early stages.

View record

 

Membership Status

Member of G+PS
View explanation of statuses

Program Affiliations

 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.