Chen G.M.,Hong Kong Polytechnic University |
Teng J.G.,Hong Kong Polytechnic University |
Chen J.F.,University of Edinburgh |
Rosenboom O.A.,Elstner Associates Inc.
Journal of Composites for Construction | Year: 2010
RC beams shear strengthened with either fiber-reinforced polymer (FRP) U-jackets/U-strips or side strips commonly fail due to debonding of the bonded FRP shear reinforcement. As such debonding occurs in a brittle manner at relatively small shear crack widths, some of the internal steel stirrups may not have reached yielding. Consequently, the yield strength of internal steel stirrups in such a strengthened RC beam cannot be fully used. In this paper, a computational model for shear interaction between FRP strips and steel stirrups is first presented, in which a general parabolic crack shape function is employed to represent the widening process of a single major shear crack in an RC beam. In addition, appropriate bond-slip relationships are adopted to accurately depict the bond behavior of FRP strips and steel stirrups. Numerical results obtained using this computational model show that a substantial adverse effect of shear interaction generally exists between steel stirrups and FRP strips for RC beams shear strengthened with FRP side strips. For RC beams shear strengthened with FRP U-strips, shear interaction can still have a significant adverse effect when FRP strips with a high axial stiffness are used. Therefore, for accurate evaluation of the shear resistance of RC beams shear strengthened with FRP strips, this adverse effect of shear interaction should be properly considered in design. © 2010 ASCE.
Schmidt M.K.,Elstner Associates Inc.
Challenging Glass 2 - Conference on Architectural and Structural Applications of Glass, CGC 2010 | Year: 2010
Heat-strengthened glass with residual surface compressive stresses above those allowed by ASTM C1048 was installed in a curtain wall in the mid-Atlantic region of the United States. To address building ownership's concerns regarding postbreakage glass fallout, fragmentation tests were performed using a protocol adapted from EN 1863. Consistent with previous research, no significant difference in fragmentation was noted between samples with residual surface compressive stresses conforming to ASTM C1048 and those with residual surface compressive stresses well beyond the established ASTM limits. Simplistic analyses revealed that, under certain modes of failure, risk of glass fallout is comparable for conforming and nonconforming heat-strengthened glass. The completed testing also has implications for glass quality control processes. Copyright © with the authors. All rights reserved.
Chin I.R.,Elstner Associates Inc. |
Heidbrink F.D.,Elstner Associates Inc.
ASTM Special Technical Publication | Year: 2014
During manufacture, fired clay units (brick, clay tile, quarry tile, terra cotta, etc.) are fired at temperatures that may vary up to approximately 2400°F (1316°C). Immediately after firing, the moisture content of fired clay units is at the lowest level they will ever be due to exposure to the high firing temperatures. This loss of moisture causes the clay to shrink during firing. Consequently, immediately after firing, fired clay units are the smallest they will ever be. After removal from the kiln, fired clay units begin to expand as a result of absorption of moisture from rain, snow, and/or humidity in the air. Under exposure to normal weathering conditions, this moisture expansion is a permanent and irreversible increase in size of the units. Moisture expansion of fired clay units that is not properly accommodated for in design and/or construction has caused adverse fracturing of the units and/or collapse of walls. Currently, there is no ASTM test procedure for measuring moisture expansion of brick and other fired clay units before or after the units are placed in service. Since the early 1960s, several papers have been prepared and published by researchers on moisture expansion of brick and clay tile. Review of readily available published papers has revealed that information on moisture expansion is sometimes conflicting. However, based upon published information reviewed and upon recent research performed, the authors present a laboratory test to estimate potential moisture expansion of newly fired clay units. In addition, a practical procedure to estimate past and future moisture expansion of fired clay units in service is presented. Copyright © 2014 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
Gems E.A.,Elstner Associates Inc. |
Will R.L.,Elstner Associates Inc.
ASTM Special Technical Publication | Year: 2014
The advent of the skeletal frame structural system and the use of terra cotta to clad skyscraper facades in the late 19th century introduced a new set of challenges, including how to accommodate the issues caused by the differential movement and volumetric changes between the steel or reinforced-concrete structural frame and the expansive clay cladding materials. The opposing forces such as frame shrinkage and the expansion of clay materials were further exacerbated by the growing heights of buildings. Although the distress caused by the differential movement in masonry-clad skyscrapers has been a long-known issue, preservation professionals have addressed this issue using different methods. Several key lessons have been learned from the various approaches over the last 40 years. One common technique for accommodation of the differential movement is known as strain relief. In the mid-1970s, this method was used at the Woolworth Building in New York City, which is an early and widely published example of the strain-relief technique described below. Stress relief in masonry-clad skyscrapers usually begins with a series of strain tests that are used to measure compressive stresses, which exist in the cladding portion of the facade. These tests involve adhering carbon-filament strain gauges to the cladding surface and then releasing the in situ stress by saw cutting around the gauged facade area. The strain value is measured before and after saw cutting, and the in situ residual facade stress is computed by multiplying the modulus of elasticity of the facade material by the measured strain change. This technique is particularly useful to determine the potential for cracking or compression failure of masonry facades. Compression failure is caused by the combination of axial load and bending associated with inelastic bucking of a brittle material such as clay masonry. Compression failure may result in outward lateral deformations, and subsurface failures, such as face shearing caused by inadequate support of the cladding. Once the stresses are computed from the strain testing, the design professional may suggest cutting horizontal relief joints into the facade at regular intervals to alleviate some of the locked-in stresses. This process has been used with varying degrees of success on terra cotta-clad facades with both steel and reinforced-concrete frames. The varied results are likely a reflection of the variations in the terra cotta material properties, restraints, unanticipated stress concentrations, and general behavior structure, which are unique to each building in general and specific to facade areas. This paper will generally explore the process of strain relief, what has been learned from the early strain-relief theories used at the Woolworth Building in 1976, and how these "lessons learned" have been implemented by the authors on various terra cotta building facades throughout the country to help preserve the urban fabric of our cities. This paper, by means of specific case studies highlighting terra cotta-clad skyscrapers, will also illustrate how one aspect of the preservation practice in facade repair and restoration, such as strain relief, while seemingly formulaic and scientific, often produces significantly varied results. Copyright © 2014 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
Duntemann J.,Elstner Associates Inc. |
Greve B.,Elstner Associates Inc.
IABSE Conference, Geneva 2015: Structural Engineering: Providing Solutions to Global Challenges - Report | Year: 2015
The twin towers of Marina City were the tallest reinforced concrete buildings in the world when they were completed in 1962. The design and construction of Marina City was an important milestone during the evolution of concrete high-rise construction during the 20th century, and the unique modern design served as a model for mixed-use developments that is still used today. The construction of the towers utilized innovative design and construction techniques. Significant concrete deterioration was identified on the facade in the 1990's which presented challenges associated with performing concrete repairs on high-rise buildings. This paper reviews the history of the design, construction and restoration of these iconic towers.
Reins J.D.,Elstner Associates Inc.
Journal of Performance of Constructed Facilities | Year: 2016
This paper discusses the partial collapse of John Purdue Block, a historic masonry structure in Lafayette, Indiana. The collapse occurred while the structure was being renovated and modified to prepare it for a new occupancy and usage. Prior to the start of the project, masonry strengths were not assessed or even estimated, and the primary structural elements were not analyzed for the proposed changes in loading and geometry. Relatively modest loads on the masonry walls and columns, coupled with a long-term performance without distress, may have provided a false sense of confidence that the structure could safely withstand comparatively minor changes in geometry and loading. Subsequent testing and analysis revealed the cause of the failure to be localized compressive stresses that exceeded the ultimate capacity of the brick masonry. © 2014 American Society of Civil Engineers.
Horst M.,Elstner Associates Inc.
ASTM Special Technical Publication | Year: 2016
Exterior insulation and finish systems (EIFS) can provide a durable, waterresistant covering for a variety of building types. However, as with any cladding material, considerations during design and workmanship during construction are the primary factors in determining the success of an EIFS-clad building. Among the important factors to consider in the design of EIFS cladding is that the EIFS is only one component of the overall building enclosure system, which includes roofing, windows, sealants, possibly other cladding materials, and many other elements. During the design phase of a project, careful consideration must be given to the compatibility of other enclosure components with the EIFS. In addition, detailing of the interfaces between the EIFS and these components, typically referred to as integration details, is critical in achieving the expected building performance and durability of the exterior cladding assembly. During the construction phase, coordination of various trades, including the EIFS installer, is essential to ensuring successful installation of these integration details. Over the past 15 years, the author has had the opportunity to evaluate a variety of EIFS-clad buildings that exhibit successes and failures of these integration details. More recently, the author has performed peer reviews for design architects and has provided consulting services to assist contractors with potential compatibility issues and with developing integration details. In this paper, the author will discuss several common problematic interfaces between EIFS and adjacent construction. Design principles and other considerations for improving the function of the exterior building enclosure at these interfaces will be explored. Several case studies, including positive and negative examples of design and construction details, will be used to illustrate concerns with their integration. In addition, the paper will identify and discuss facets of several of the standards that have been developed by ASTM International (ASTM) to assist designers, consultants, and contractors in the development of integration details and the determination of their compatibility. © Copyright 2016 by ASTM International.
Kehoe B.E.,Elstner Associates Inc.
9th US National and 10th Canadian Conference on Earthquake Engineering 2010, Including Papers from the 4th International Tsunami Symposium | Year: 2010
There are a number of standards and methodologies available for the seismic evaluation of existing buildings. Some of these standards are intended to be used for specific building types, such as unreinforced masonry buildings, while other standards are intended to be applied to more general types of buildings. ASCE 31-03 has evolved over time through a series of earlier guidelines and is a standard that has been developed to be applied to a variety of building types. Each seismic evaluation method that has been developed has a specific purpose and audience for which it has been targeted. As such, these methodologies have advantages and limitations. While some limitations are obvious, others are more fundamental and not as apparent. Some of these fundamental limitations with respect to ASCE 31-03 are discussed. In addition to limitations in the applicability of the methodology within the ASCE 31-03 standard, there are issues with how the standard correlates with other design and evaluation standards that are currently in use. Recommendations are made to changes in the basic concept of ASCE 31-03, which relies on standard building types based on material and lateral force resisting system, to a methodology that focuses primarily on seismic behavior. The characteristics that affect seismic behavior include height, lateral force resisting system, materials, and configuration. Different techniques can then be used to evaluate the performance of buildings for each of the behavior types.
Kehoe B.E.,Elstner Associates Inc.
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014
Seismic design of nonstructural components using ASCE 7-10 considers the interaction between the response of the nonstructural component and the response of the building by means of a component amplification factor, ap, that accounts for the dynamic interaction between the nonstructural component and the response of the building. ASCE 7-10 provides tables of architectural, mechanical, and electrical components that specify values for ap. The values in the tables are either 1.0 or 2.5 for components considered rigid or flexible, respectively. ASCE 7-10 provides a definition for determining whether a component is rigid based on the component's period of vibration. The tabulated values of nonstructural amplification factors may not adequately characterize the actual seismic behavior of some nonstructural components since the values do not consider the actual properties of the nonstructural components and the effect of actual support and bracing. While ASCE 7-10 provides a formula for determining the actual period of mechanical and electrical components, this formula is seldom used in actual practice. Determining the period of vibration of a nonstructural component does not provide all of the information needed to assess how a nonstructural component will respond during an earthquake since it does not consider the predominant periods of vibration of the building. The vibrational periods for some common nonstructural components are tabulated based on considerations of material properties and dimensions. Data from component testing are also summarized and compared to calculated values. The influence of support conditions are also described. Recommendations for changes to building code requirements are presented.
Tide R.H.R.,Elstner Associates Inc.
Engineering Journal | Year: 2010
In this paper, bolt shear capacities are reviewed using the Load and Resistance Factor Design (LRFD) philosophy. Only bolt-shear limit states are addressed, although one aspect of slip critical limit states is addressed incidentally. This paper does not consider bolt bearing limit states. Test data used to justify the adoption of ASTM A325 and A490 high-strength bolts was obtained from previous research programs. The data also included various types of rivets and Huck bolts for general comparison. First, the test data are used to evaluate the current American Institute of Steel Construction (AISC, 2005) and Research Council on Structural Connections (RCSC, 2004) bolt shear provisions and to determine the current reliability, β, which is found to be conservative when based on a resistance factor, φ, of 0.75. The appropriateness of the ?-factor for bolt shear is addressed. Canadian (CSA S16-01) and Eurocode (EN 1993) provisions are also evaluated and shown not to be compatible with the test results. Two design equations are developed-one linear, one a step function-that result in a β value slightly greater than 3.0, appropriate for a manufactured product. The single-step function (with a step at 38 in.) is recommended for inclusion in updated design specifications. This design provision increases the design strength by 12.5% for short connections and by 17.2% for long connections. The test data indicate that there is no need for a bolt strength reduction due to the length of the connection, provided that the connection material gross and net section areas exceed certain ratios. That ratio is a function of the connection material yield and tensile strength, the total bolt shear area and the bolt tensile strength.