Overview of Papers

Below is a short overview of the papers published in this volume with regard to the above five categories.

Laboratory Testing and Specialized Outdoor Exposure Testing

Over the last decade, the use of fiber-reinforced polymer (FRP) composites as construction materials in structural engineering applications has grown substantially. Also known as advanced composite materials (ACMs), these materials have proven themselves to be especially valuable for use as main components in hybrid structural members. However, in order to fully capital­ize on the high tensile strength of the FRP materials, an effective connection mechanism between the FRP and the conventional building material must be operational at the interface in order to achieve optimum performance of the hybrid structural members. Chen and El-Hacha in their paper investi­gate the bond performance between glass-fiber reinforced polymer (GFRP) plates and cast-in-place ultra-high-performance concrete (UHPC) using an epoxy-based adhesive filled with coarse silica sand aggregates. Both shear and tensile tests are conducted using three different types of epoxy adhe­sives. Analysis of the experimental data shows that the specimens bonded with the moisture tolerant epoxy adhesive intended for bonding of hardened concrete and steel performs the best.

The use of glass in the building industry is increasingly extended be­yond its space-enclosing function to structural applications, such as in glass beams, glass columns or bracing fagade elements. Recently, interest in I – shaped bonded hybrid steel-glass beams as transparent structural elements has grown. In these beams, steel flanges and glass are connected by a linear adhesive bond. The coupling between steel and glass substantially increases the flexural strength of the glass beams due to the shear forces being trans­ferred via an adhesive bond. In their contribution, Feldmann, Abeln and Preckwinkel study the behavior of adhesive joints in hybrid steel-glass beams by means of simplified small scale tests. The results show that full – scale hybrid beams with butt splice bonded and U-bonded geometries are feasible using suitable load-bearing adhesives. However, careful design of the joints is required, taking the specific properties of the adhesive (brittle­ness, weather resistance, etc.) into consideration.

Autoclaved aerated concrete (AAC), also known as autoclaved cellular con­crete (ACC) or autoclaved lightweight concrete (ALC), was invented in the mid-1920s in Sweden and has recently gained some reputation as a green building material, because of its thermal insulation property. In Japan, high – performance water-borne acrylic sealants are traditionally the sealant prod­uct of choice for use between ALC panels. While the degradation mechanisms

of acrylic sealants are well known, their resistance to outdoor weathering has not yet been fully investigated. Miyauchi, Lacasse, Enomoto, Murata and Tanaka study the long-term behavior of these sealants by on-site inves­tigation of acrylic sealed external joints of ALC-clad buildings as well as by outdoor exposure testing of different types of acrylic sealants in three climate regions located in Japan. As expected, the aging of these sealants, as deter­mined by the degree of surface cracking, depends on the local temperature and the respective degree of exposure to solar radiation. Also not surpris­ingly, joint configurations with two-sided sealant adhesion, installed in deep panel ALC cladding, are more reliable than three-sided adhesion joints used for thin panel ALC cladding in terms of the durability of the sealed joints installed in actual buildings. However, what does surprise is the substantial amount by which the elongation of the three-sided adhesive joint configura­tions decreases after five years outdoor exposure and the associated large number of sealed joints with ALC substrate failure.

The durability of sealed or bonded joints is dictated by many factors such as joint design, surface preparation, application, formulation, joint move­ment, and weather. Schueneman, Hunt, Lacher, White and Hunston at­tempt to address the link between formulation and weathering durability by monitoring changes in apparent modulus during exposure to outdoor weath­ering and cyclic strain. Cyclic movement is accomplished via custom built systems that apply cyclic strain. The conditions for simultaneous exposure to strain and weathering are chosen such as to simulate wood (cold compres­sion) and concrete/metal (hot compression) construction materials. A key finding of their research is that changes in apparent modulus are primarily driven by underlying changes in compression set, a potentially critical con­tributor to stress in structures during rapid temperature changes.

In their paper, Sitte, Brasseur, Carbary and Wolf report on the prelimi­nary evaluation of a novel transparent structural silicone adhesive (TSSA) developed for point fixing in glazing. The paper presents information on the durability and physical properties of the new material and suggests a meth­odology for deriving static and dynamic design strength values for the new material based on creep rupture experiments as well as nondestructive dy­namic load experiments using the stress whitening phenomenon observed with this material as the limit state. The paper further discusses material characterization and hyperelastic modeling used in the finite element analy­sis based on finite strain theory.

The Institute of Building Construction at Dresden’s Technical University is one of Europe’s leading research facilities focused on the study of glass in buildings. Weller and Vogt describe some of the research activities carried out at this institute on bonded glass connections for load-bearing structures. Examples of the research covered are bonded point supports for overhead

glazing and for large photovoltaic modules subjected to high environmen­tal loads, linear adhesive joints for hybrid steel-glass composite beams with good ductility and for glass fins with a reduced cross-section in minimized steel-and-glass facades, as well as bonded joints for photovoltaic facades and for an all-glass pavilion.

Further research at the same institute is highlighted in a paper by Weller, Nicklisch, Prautzsch and Vogt that outlines the testing and evaluation program used in the selection of adhesives for transparent bonded joints in all-glass load-bearing structures of two buildings located in Dresden and Grimma, Germany. The test and evaluation program designed by the insti­tute led to individual approvals of these constructions by the German build­ing code authority. The authors describe the various stages of this project from the evaluation of material properties of various adhesives to the opti­mization of the bonded joint geometry in order to achieve long-term integrity of the structures.

Recent years have seen a multitude of new sealant and adhesive products based on novel polymers, cure chemistries, and formulations being launched onto the market for which there is a lack of experience in terms of perform­ance histories for similar products. An accurate service life prediction model is urgently needed for building sealants to greatly reduce the time-to-market of a new product and reduce the risk of commercializing a poorly performing product. A key element in any accelerated weathering test is the precise con­trol of all environmental variables in the laboratory test apparatus in order to produce reliable weathering data that can be used to generate a predictive model. In their contribution, White, Hunston, Tan, Filliben, Pintar and Schueneman report on a systematic study investigating individual and synergistic impacts of four environmental factors (cyclic movement, tem­perature, relative humidity, and ultraviolet radiation) on the durability of a model sealant using a novel laboratory test apparatus. The apparatus not only allows precise control of the environmental factors, but it also permits in-situ characterization tests of the specimens.