Accurate identificationof the surface area of threaded fas teners is essential for understanding... more Accurate identificationof the surface area of threaded fas teners is essential for understanding the behavior of fasteners in numerous applications. For example, the surface area of a threaded fastener is needed to properly calculate its corrosion rate. Followingthe voluntary withdrawal of CCA (chromated copper arsenate)from residentialuse, alkalinewood preserva tives such as ACQ (alkaline copper quarternary) and CuAz (alkaline copper azole) are being increasingly used. These new alkaline-based preservatives are more corrosive than CCA, but little is known about their corrosion rates on threaded fasteners in contact with the treated wood. This is in part due to the fact that up until now no general analytical expression of the surface area of threaded fasteners existed so previous corrosion rate calculations were imprecise. With increasing environmental regulations, it is likely wood preservatives will be modified on a more frequent basis, requiring a revaluationof the corrosionpo...
This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this re... more This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this research is to better understand the conditions of heat delamination in cross laminated timber (CLT) that is exposed to fire. Heat delamination in CLT occurs when one lamination detaches from the composite panel before the char front reaches the bondline. Timber that falls from the panel, as a result of delamination, contributes additional fuel to the fire, which can cause fire regrowth, while the loss of a lamination causes a sudden loss in strength. Currently, to demonstrate that an adhesive does not delaminate, it must pass a full scale (6 m by 3 m) compartment fire test as prescribed in the PRG-320 product standard. In this work, we scaled down the mechanical loads and temperatures to 300 mm lap shear specimens. Seven different adhesives were tested and compared against solid wood controls with the same geometry as the lap shear specimens. Quasi-static tests were run where the specimen...
Various design approaches for establishing the resistance of connections in cross-laminated timbe... more Various design approaches for establishing the resistance of connections in cross-laminated timber (CLT) structures have been developed and adopted in timber design standards worldwide. Although the fundamental principles are similar, the new design provisions for CLT connections have been aligned in some standards with the existing design philosophy and format adopted for sawn timber and glulam using traditional fasteners such as dowels, nails, and wood screws for consistency and simplicity, in the other standards, alternate approaches have been developed. This article presents a snap shot of the various design approaches for connections in CLT adopted in Europe, Canada, the United States, and New Zealand. The intent is for the reader to have a better knowledge of the underpinning assumptions, principles, and the adopted design rules in each of these standards.
This study reviewed the literature on static and impact withdrawal of nails driven into the end g... more This study reviewed the literature on static and impact withdrawal of nails driven into the end grain of wood members. From this, an empirical relationship was created relating the specific gravity of the wood, the diameter of the nail, and the depth of penetration of the nail to the static withdrawal capacity of nails driven into the wood and withdrawn immediately. Areas of additional research are identified for end-grain nailing in wood members.
Soft-story wood-frame buildings have been recognized as a disaster preparedness problem for decad... more Soft-story wood-frame buildings have been recognized as a disaster preparedness problem for decades. There are tens of thousands of these multi-family three-and four-story structures throughout California and other cities in the United States. The majority were constructed between 1920 and 1970, with many being prevalent in the San Francisco Bay Area in California. The NEES-Soft project was a five-university multi-industry effort that culminated in a series of full-scale soft-story wood-frame building tests to validate retrofit philosophies proposed by (1) the Federal Emergency Management Agency (FEMA) P-807 guidelines and (2) a performance-based seismic retrofit (PBSR) approach developed within the project. Four different retrofit designs were developed and validated at full-scale, each with specified performance objectives, which were typically not the same. This paper focuses on the retrofit design using cross laminated timber (CLT) rocking panels and presents the experimental results of the full-scale shake table test of a four-story 370 m 2 (4000 ft 2) soft-story test building with that FEMA P-807 focused retrofit in place. The building was subjected to the 1989 Loma Prieta and 1992 Cape Mendocino ground motions scaled to 5% damped spectral accelerations ranging from 0.2 to 0.9 g.
Electrical impedance spectra (EIS) were collected from southern pine (Pinus spp.) wood equilibrat... more Electrical impedance spectra (EIS) were collected from southern pine (Pinus spp.) wood equilibrated to 12% moisture content. Cylindrical graphite electrodes were embedded in the wood so that they met nearly end-to-end along a line parallel to the grain, and the EIS properties were characterized as functions of electrode spacing and electrode contact pressure at frequencies between 1 × 10 −1 and 3 × 10 5 Hz. The data show a narrow distribution of relaxation times, which can be fit using a Debye model or, even better, a model with a constant phase element (CPE) in parallel with a resistor. The relaxation time is sensitive to contact pressure applied to the electrodes but not electrode spacing. The width of the CPE distribution is sensitive to electrode spacing but not contact pressure. On first inspection, the data suggest a finite contact resistance between wood and electrode, but further examination reveals that the "contact resis tance" is an artifact caused by electrode fringe effects.
ABSTRACT The existence of thousands of soft-story woodframe buildings in California has been reco... more ABSTRACT The existence of thousands of soft-story woodframe buildings in California has been recognized as a disaster preparedness problem resulting in mitigation efforts throughout the state. The considerable presence of these large multi-family buildings in San Francisco prompted the city to mandate their retrofitting over the next seven years. The NEES-Soft project, whose full title is “Seismic Risk Reduction for Soft- Story Woodframe Buildings,” is a five-university multi-industry three-year project which has many facets including improved nonlinear numerical modeling, outreach, retrofit methodology development, and full-scale system-level experimental validation of soft-story retrofit techniques. In 2013, two full-scale buildings were tested within NEES-Soft. A hybrid test of a three-story building consisting of a onestory numerical substructure and a two-story physical structure above at the University at Buffalo, and a shake table test of a four-story building at the University of California – San Diego. A series of retrofits, based on methodologies ranging from FEMA P-807 to performance-based seismic retrofits developed as part of the project, were tested at both sites. Collapse testing for both building specimens was also conducted at the end of each test program. This paper presents a summary of selected test results for these full-scale building tests within the NEES-Soft project.
Chromated copper arsenate (CCA), the most widely used wood preservative of the past 50 years, has... more Chromated copper arsenate (CCA), the most widely used wood preservative of the past 50 years, has been replaced for most uses with alkaline-copper systems such as alkaline copper quaternary (ACQ), copper azole (CuAz) and micronized copper quaternary (MCQ). Preliminary research using high-temperature, high-humidity environments have shown that some of these wood preservatives are more corrosive than CCA, although it is unclear how the results of these extreme tests correlate to performance at temperatures and humidities seen in-service. Recently, the authors developed an electrochemical method for rapid determination of the corrosion rate for fasteners in water extracts of treated wood. The authors have previously demonstrated good correlation between the electrochemical-extract test and exposure tests of fasteners in ACQ treated Southern pine. This work uses the electrochemical-extract method to examine corrosion of carbon steel and galvanized steel on untreated southern pine, as well as southern pine treated with five different wood preservatives.
Summary In the 2001 National Design Specifications® for Wood Construction (NDS), Appendix E was a... more Summary In the 2001 National Design Specifications® for Wood Construction (NDS), Appendix E was added to explicitly address wood failure mechanisms that may occur in fasteners. One approach to estimate design capacities for net section, row tear out, and ...
ABSTRACT There are thousands of soft-story wood-frame buildings in California which have been rec... more ABSTRACT There are thousands of soft-story wood-frame buildings in California which have been recognized as a disaster preparedness problem with concerted mitigation efforts underway in many cities throughout the state. The vast majority of those efforts are based on numerical modelling, often with half-century old data in which assumptions have to be made based on engineering judgment and project committee consensus. The NEES-Soft project, whose full title is "Seismic Risk Reduction for Soft-Story Wood-frame Buildings," is a five-university multi-industry three-year project with many facets including improved nonlinear numerical modelling, outreach, design method development, and full-scale system-level experimental validation of soft-story retrofit techniques. In 2013, two full-scale buildings were tested within NEES-Soft. The first was a three-story building tested at the University at Buffalo NEES facility using slow pseudo-dynamic testing. The bottom story, representing a soft story with garage openings, was the numerical substructure reproduced by computer, while the damage to the two upper stories, representing the physical substructure, was observed in the lab and provided feedback to the actuators. This test had the main objective of determining the effect of the retrofits on damage to the upper stories and collapse risk of the complete structure. The second major test was on a full-scale four-story 400 square meter soft-story building. It was tested by the NEES-Soft project team at the UCSD NEES outdoor shake table facility using a variety of retrofits. These retrofits ranged from FEMA P-807 retrofits to performance-based seismic retrofits developed as part of the project. Both tests demonstrated the effectiveness of the FEMA P-807 retrofit guidelines and the NEES-UCSD test validated the PBSR methodology developed within the NEES-Soft project.
Http Dx Doi Org 10 1080 13632469 2014 975896, Oct 14, 2014
ABSTRACT The FEMA P-807 Guidelines were developed for retrofitting soft-story wood-frame building... more ABSTRACT The FEMA P-807 Guidelines were developed for retrofitting soft-story wood-frame buildings based on existing data, and the method had not been verified through full-scale experimental testing. This article presents two different retrofit designs based directly on the FEMA P-807 Guidelines that were examined at several different seismic intensity levels. The effects of the retrofits on damage to the upper stories were investigated. The results from the hybrid testing verify that designs following the FEMA P-807 Guidelines meet specified performance levels and appear to successfully prevent collapse at significantly higher seismic intensity levels well beyond for which they were designed. Based on the test results presented in this article, it is recommended that the soft-story-only retrofit procedure can be followed when financial or other constraints limit the retrofit from bringing the soft-story building up to current code or applying performance-based procedures.
Accurate identificationof the surface area of threaded fas teners is essential for understanding... more Accurate identificationof the surface area of threaded fas teners is essential for understanding the behavior of fasteners in numerous applications. For example, the surface area of a threaded fastener is needed to properly calculate its corrosion rate. Followingthe voluntary withdrawal of CCA (chromated copper arsenate)from residentialuse, alkalinewood preserva tives such as ACQ (alkaline copper quarternary) and CuAz (alkaline copper azole) are being increasingly used. These new alkaline-based preservatives are more corrosive than CCA, but little is known about their corrosion rates on threaded fasteners in contact with the treated wood. This is in part due to the fact that up until now no general analytical expression of the surface area of threaded fasteners existed so previous corrosion rate calculations were imprecise. With increasing environmental regulations, it is likely wood preservatives will be modified on a more frequent basis, requiring a revaluationof the corrosionpo...
This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this re... more This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this research is to better understand the conditions of heat delamination in cross laminated timber (CLT) that is exposed to fire. Heat delamination in CLT occurs when one lamination detaches from the composite panel before the char front reaches the bondline. Timber that falls from the panel, as a result of delamination, contributes additional fuel to the fire, which can cause fire regrowth, while the loss of a lamination causes a sudden loss in strength. Currently, to demonstrate that an adhesive does not delaminate, it must pass a full scale (6 m by 3 m) compartment fire test as prescribed in the PRG-320 product standard. In this work, we scaled down the mechanical loads and temperatures to 300 mm lap shear specimens. Seven different adhesives were tested and compared against solid wood controls with the same geometry as the lap shear specimens. Quasi-static tests were run where the specimen...
Various design approaches for establishing the resistance of connections in cross-laminated timbe... more Various design approaches for establishing the resistance of connections in cross-laminated timber (CLT) structures have been developed and adopted in timber design standards worldwide. Although the fundamental principles are similar, the new design provisions for CLT connections have been aligned in some standards with the existing design philosophy and format adopted for sawn timber and glulam using traditional fasteners such as dowels, nails, and wood screws for consistency and simplicity, in the other standards, alternate approaches have been developed. This article presents a snap shot of the various design approaches for connections in CLT adopted in Europe, Canada, the United States, and New Zealand. The intent is for the reader to have a better knowledge of the underpinning assumptions, principles, and the adopted design rules in each of these standards.
This study reviewed the literature on static and impact withdrawal of nails driven into the end g... more This study reviewed the literature on static and impact withdrawal of nails driven into the end grain of wood members. From this, an empirical relationship was created relating the specific gravity of the wood, the diameter of the nail, and the depth of penetration of the nail to the static withdrawal capacity of nails driven into the wood and withdrawn immediately. Areas of additional research are identified for end-grain nailing in wood members.
Soft-story wood-frame buildings have been recognized as a disaster preparedness problem for decad... more Soft-story wood-frame buildings have been recognized as a disaster preparedness problem for decades. There are tens of thousands of these multi-family three-and four-story structures throughout California and other cities in the United States. The majority were constructed between 1920 and 1970, with many being prevalent in the San Francisco Bay Area in California. The NEES-Soft project was a five-university multi-industry effort that culminated in a series of full-scale soft-story wood-frame building tests to validate retrofit philosophies proposed by (1) the Federal Emergency Management Agency (FEMA) P-807 guidelines and (2) a performance-based seismic retrofit (PBSR) approach developed within the project. Four different retrofit designs were developed and validated at full-scale, each with specified performance objectives, which were typically not the same. This paper focuses on the retrofit design using cross laminated timber (CLT) rocking panels and presents the experimental results of the full-scale shake table test of a four-story 370 m 2 (4000 ft 2) soft-story test building with that FEMA P-807 focused retrofit in place. The building was subjected to the 1989 Loma Prieta and 1992 Cape Mendocino ground motions scaled to 5% damped spectral accelerations ranging from 0.2 to 0.9 g.
Electrical impedance spectra (EIS) were collected from southern pine (Pinus spp.) wood equilibrat... more Electrical impedance spectra (EIS) were collected from southern pine (Pinus spp.) wood equilibrated to 12% moisture content. Cylindrical graphite electrodes were embedded in the wood so that they met nearly end-to-end along a line parallel to the grain, and the EIS properties were characterized as functions of electrode spacing and electrode contact pressure at frequencies between 1 × 10 −1 and 3 × 10 5 Hz. The data show a narrow distribution of relaxation times, which can be fit using a Debye model or, even better, a model with a constant phase element (CPE) in parallel with a resistor. The relaxation time is sensitive to contact pressure applied to the electrodes but not electrode spacing. The width of the CPE distribution is sensitive to electrode spacing but not contact pressure. On first inspection, the data suggest a finite contact resistance between wood and electrode, but further examination reveals that the "contact resis tance" is an artifact caused by electrode fringe effects.
ABSTRACT The existence of thousands of soft-story woodframe buildings in California has been reco... more ABSTRACT The existence of thousands of soft-story woodframe buildings in California has been recognized as a disaster preparedness problem resulting in mitigation efforts throughout the state. The considerable presence of these large multi-family buildings in San Francisco prompted the city to mandate their retrofitting over the next seven years. The NEES-Soft project, whose full title is “Seismic Risk Reduction for Soft- Story Woodframe Buildings,” is a five-university multi-industry three-year project which has many facets including improved nonlinear numerical modeling, outreach, retrofit methodology development, and full-scale system-level experimental validation of soft-story retrofit techniques. In 2013, two full-scale buildings were tested within NEES-Soft. A hybrid test of a three-story building consisting of a onestory numerical substructure and a two-story physical structure above at the University at Buffalo, and a shake table test of a four-story building at the University of California – San Diego. A series of retrofits, based on methodologies ranging from FEMA P-807 to performance-based seismic retrofits developed as part of the project, were tested at both sites. Collapse testing for both building specimens was also conducted at the end of each test program. This paper presents a summary of selected test results for these full-scale building tests within the NEES-Soft project.
Chromated copper arsenate (CCA), the most widely used wood preservative of the past 50 years, has... more Chromated copper arsenate (CCA), the most widely used wood preservative of the past 50 years, has been replaced for most uses with alkaline-copper systems such as alkaline copper quaternary (ACQ), copper azole (CuAz) and micronized copper quaternary (MCQ). Preliminary research using high-temperature, high-humidity environments have shown that some of these wood preservatives are more corrosive than CCA, although it is unclear how the results of these extreme tests correlate to performance at temperatures and humidities seen in-service. Recently, the authors developed an electrochemical method for rapid determination of the corrosion rate for fasteners in water extracts of treated wood. The authors have previously demonstrated good correlation between the electrochemical-extract test and exposure tests of fasteners in ACQ treated Southern pine. This work uses the electrochemical-extract method to examine corrosion of carbon steel and galvanized steel on untreated southern pine, as well as southern pine treated with five different wood preservatives.
Summary In the 2001 National Design Specifications® for Wood Construction (NDS), Appendix E was a... more Summary In the 2001 National Design Specifications® for Wood Construction (NDS), Appendix E was added to explicitly address wood failure mechanisms that may occur in fasteners. One approach to estimate design capacities for net section, row tear out, and ...
ABSTRACT There are thousands of soft-story wood-frame buildings in California which have been rec... more ABSTRACT There are thousands of soft-story wood-frame buildings in California which have been recognized as a disaster preparedness problem with concerted mitigation efforts underway in many cities throughout the state. The vast majority of those efforts are based on numerical modelling, often with half-century old data in which assumptions have to be made based on engineering judgment and project committee consensus. The NEES-Soft project, whose full title is "Seismic Risk Reduction for Soft-Story Wood-frame Buildings," is a five-university multi-industry three-year project with many facets including improved nonlinear numerical modelling, outreach, design method development, and full-scale system-level experimental validation of soft-story retrofit techniques. In 2013, two full-scale buildings were tested within NEES-Soft. The first was a three-story building tested at the University at Buffalo NEES facility using slow pseudo-dynamic testing. The bottom story, representing a soft story with garage openings, was the numerical substructure reproduced by computer, while the damage to the two upper stories, representing the physical substructure, was observed in the lab and provided feedback to the actuators. This test had the main objective of determining the effect of the retrofits on damage to the upper stories and collapse risk of the complete structure. The second major test was on a full-scale four-story 400 square meter soft-story building. It was tested by the NEES-Soft project team at the UCSD NEES outdoor shake table facility using a variety of retrofits. These retrofits ranged from FEMA P-807 retrofits to performance-based seismic retrofits developed as part of the project. Both tests demonstrated the effectiveness of the FEMA P-807 retrofit guidelines and the NEES-UCSD test validated the PBSR methodology developed within the NEES-Soft project.
Http Dx Doi Org 10 1080 13632469 2014 975896, Oct 14, 2014
ABSTRACT The FEMA P-807 Guidelines were developed for retrofitting soft-story wood-frame building... more ABSTRACT The FEMA P-807 Guidelines were developed for retrofitting soft-story wood-frame buildings based on existing data, and the method had not been verified through full-scale experimental testing. This article presents two different retrofit designs based directly on the FEMA P-807 Guidelines that were examined at several different seismic intensity levels. The effects of the retrofits on damage to the upper stories were investigated. The results from the hybrid testing verify that designs following the FEMA P-807 Guidelines meet specified performance levels and appear to successfully prevent collapse at significantly higher seismic intensity levels well beyond for which they were designed. Based on the test results presented in this article, it is recommended that the soft-story-only retrofit procedure can be followed when financial or other constraints limit the retrofit from bringing the soft-story building up to current code or applying performance-based procedures.
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Papers by DOUGLAS RAMMER