This document outlines the basis of design for the performance-based design and nonlinear response history analysis of the Framework Project in Portland, OR. Performance-based design is pursued for this project because the proposed lateral force-resisting system, consisting of post-tensioned rocking cross-laminated timber (CLT) walls is not included in ASCE/SEI 7-10 Table 12.2-1.
Nationwide, bridges are deteriorating at a rate faster than they can be rehabilitated and maintained. This has resulted in a search for new methods to rehabilitate, repair, manage, and construct bridges. As a result, structural health monitoring and smart structure concepts have emerged to help improve bridge management. In the case of timber bridges, however, a limited amount of research as been conducted on long-term structural health monitoring solutions, and this is especially true in regards to historic covered timber bridges. To date, evaluation efforts of timber bridges have focused primarily on visual inspection data to determine the structural integrity of timber structures. To fill this research need and help improve timber bridge inspection and management strategies, a 5-year research plan to develop a smart timber bridge structure was undertaken. The overall goal of the 5-year plan was to develop a turnkey system to analyze, monitor, and report on the performance and condition of timber bridges. This report outlines one phase of the 5-year research plan and focuses on developing and attaching moisture sensors onto timber bridge components. The goal was to investigate the potential for sensor technologies to reliably monitor the in situ moisture content of the timber members in historic covered bridges, especially those recently rehabilitated with glulam materials. The timber-specific moisture sensors detailed in this report and the data collected from them will assist in advancing the smart timber bridge.
In this study, the duration-of-load effect on the rolling shear strength of cross laminated timber (CLT), with different cross-sectional layups (five-layer and three-layer), was evaluated. A stress-based damage accumulation model is chosen to evaluate the duration-of-load strength adjustment factor of the rolling shear strength of CLT. This model incorporates the established short-term rolling shear strength of material and predicts the time to failure under arbitrary loading history. The model has been calibrated and verified based on the test data from low cycle trapezoidal fatigue tests (damage accumulation tests) in the previous study. The long-term rolling shear behaviour of CLT can then be evaluated from this verified model. As the developed damage accumulation model is a probabilistic model, it can be incorporated into a time based reliability assessment of the CLT products, considering short-term, snow, and dead load only loading cases. The reliability analysis results and factors reflecting the duration-of-load effect on the rolling shear strength of CLT are compared and discussed. The characteristic of this modeling theory lies in that the verified model is also able to predict the duration-of-load behaviour of CLT products under arbitrary loading history, such as long-term dead load case; then, these predictions of time to failure from the damage accumulation model can elucidate duration of load by the stress ratio evaluation approach. The results suggest that the duration-of-load rolling shear strength adjustment factor for CLT is more severe than the general duration-of-load adjustment factor for lumber; this difference should be considered in the introduction of CLT into the building codes for engineered wood design.
A major concern with tall wood buildings is fire during or after an earthquake. Through a survey of factors including reliability of systems, reliability of water supplies, availability of professional and civilian fire fighting, the paper will examine the overall reliability of sprinkler systems in including assessment of the ability untrained fire fighters to suppress fires in a timber high-rise in the absence of professional fire fighters. A probability based fault tree analysis will provide guidance designers of tall wood buildings in providing acceptable fire safety after a seismic event.
This paper discusses the principles of performance based structural design and motivates the need for probabilistic assessment of the response of structures and an assessment of the consequences of failure. Using the results from a series of tests carried out at SP in Sweden, we extrapolate data required for the assessment of timber structures under a range of parametric fires. This data also includes information required to develop probabilistic models of the response of timber elements under different parametric fires. Using methodologies from the literature, we then carry out a reliability analysis of timber structures, considering uncertainties the timber response to fire. This is carried out using the first order reliability method. We show that the opening factor has an influence on the reliability of timber structures, as a result of the rate of heating in a parametric fire exposure. A minimum reliability, evolving over time, is seen to occur at an opening factor of 0.14m 1/2.
Finally, we propose a modification to the Eurocode target reliability indices that allows these to be used as a target reliability index for structures exposed to fire. The proposed modification is dependent on the floor area and the method is exemplified here for a range of floor areas and its application to timber structures is illustrated.
Society of Wood Science and Technology International Convention
Failure modes of Cross Laminated Timber (CLT) plates reach by an excess of tensile stress on
finger joints, shear stress on transverse layer due to rolling shear effect and by natural
vibration. The Probability of Failure (POF) of CLT plates can be estimated from the probability
distribution of their ruptures and stiffnesses, as well as their correlation coefficients. In this
context, the aim of this paper is to estimate the load capacity of Cross Laminated Timber plates
from a specific probability of failure and the experimental results of mechanical and physical
properties. For this purpose, CLT plates were manufactured with wood species of Pinus taeda
L., from Brazilian reforestation plantations. Four-point bending tests were conducted to
investigate the failure behavior of the CLT plates. Density and moisture content were obtained
from small specimens extracted from these plates. Monte Carlo simulation was carried out to
predict the probabilistic loads that produce the failure of CLT plates, considering the failure
occasioned by natural vibration as well. Experimental and numerical results of the failure
modes were compared and the maximum loads to an acceptable probability of failure of the
several CLT lengths were estimated too.