2010

This paper examines the operation and performance of a recently constructed 14 storey double façade building located in downtown Toronto, Ontario at the University of Toronto campus. 

The goal of the investigation was to compare intended performance with measured performance of the double façade assembly.  To achieve this, data from continued temperature monitoring was compared to the simulation results obtained from an industry tested finite element building simulation software.  Original design assumptions were reviewed and compared to the as-built construction.  Observations of a design modification involving compartmentalization between floors appears to have reduced the energy savings potential of the double façade.  Occupant surveys were conducted to gather qualitative data on thermal comfort. Operation of the as-built construction was simulated and compared to reported building energy consumption data provided by operations staff. 

Based on this comparison, a series of recommendations are provided that can improve the performance of the double façade assembly.

As the focus of new building construction shifts towards sustainability with emphasis on energy efficient design, more importance is placed on performance of the building envelope. Ensuring the envelope performs up to specifications is, at least in part, the purview of whole building commissioning. Government developments in Canada and the United States have been commissioning the building envelope for many years. Commissioning is becoming more common in the commercial sector, as developers require more specific project targets, either to meet enhanced building code requirements or earn LEED certification.

However, no amount of physical testing or field observation can compensate for an envelope who’s design was flawed from the outset. It is therefore important for building scientists to support a project’s design with quantitative data, prior to construction commencing. Computer simulation programs aid in this respect, giving building scientists the ability to model simulations that would be difficult to calculate otherwise. Simulations provide the ability to quickly verify a design’s expected performance, highlight problem areas for revision by the principal designers, or predict potential long term problems in novel, un-tried assemblies.

This paper focuses on several case studies where thermal analysis and hygrothermal simulation software aided in the evaluation and adjustment of several building envelope designs. The software aided the commissioning process in several ways.

Tall timber Pagoda was very popular at one time in ancient China. The Yingxian Wooden Pagoda is an example of such building which survived close to 1000 years of exposure to the elements and forces of nature, wars, and human usage as well as misuse. This paper discusses many unique structural features of this Pagoda building by relating its special structural form and structural elements to its ability to resist large seismic forces.

Introduction

Timber was one of the most important building materials in China. It was used as roof, floor, and column members in most buildings including common residences, large villas for the affluent, ancestral halls, temples, and palaces. Nowadays timber is seldom used as prime structural components in modern Chinese construction even though there is an unprecedented construction boom since the late 1980s. The main reason for this dilemma is that the unsustainable depletion of domestic wood supply in the 1950s–1970s led to logging moratorium for several decades.

Without domestic wood supply, timber engineering education in universities ceased further leading to common misconceptions of wood as structural material. Nevertheless, there are still many examples of these ancient Chinese timber structures, which have withstood centuries of exposure to the elements and forces of nature, survived many wars, and endued human usage as well as misuse. It is important to study the past and examine some of these structures in detail as we progress into future novel applications of timber systems. Of particular interest are the ancient tall timber structures, the pagodas.

In urban cities, underground tunnels and stations for rapid transit systems are commonly buried underground. Compared with cantilever above-grade structures, underground stations have performed relatively well in past earthquakes. This may be attributed to the unique service conditions of underground stations- lateral support by surrounding soils. Station designers need to consider the interaction with surrounding soils for earthquake loading.

Seismic design methods for underground stations are different from that of cantilever above-grade structures. Shear distortion is typically believed to be the major concern for underground structures. Three methods are discussed here: the dynamic earth pressure methods, the free-field racking deformation method and the soil-structure interaction methods. The advantages and disadvantages of these methods are compared and summarized.

Two models were employed in designing the Canada Line Stations in Vancouver, British Columbia, Canada. Both of the models originated from the dynamic earth pressure methods with the consideration of shear racking deformation. The first model assumes that dynamic earth pressure is transferred to the base by a moment frame consisting of walls and slabs. The whole structure is assumed to sit at the base. This model was for structures built in complicated soil condition, such as a station half-buried in the bedrock and half buried in the soft soil. In the second model, free-field racking deformation is used to check major structural members and joints first. Then the slabs and walls are designed to sustain the dynamic and static soil pressures. Moment redistribution at joints is considered to minimize the wall and slab thickness. All soil pressures are assumed to be transferred to the other side by slabs and resisted by the passive pressure. The concept of this model is to produce a flexible structure to move together with seismic shear wave. This model can produce more economical design than the first model. Both models were used in designing different stations.

The design of a 84 m-long 6.7 m-wide one-storey residence built on an island off the coast of British Columbia, Canada presented special timber engineering challenges. To use materials that can be easily transported in pieces and built on site, panel web beams (PWB) were developed as main structural components. The PWB utilizes 130 mm x 300 mm Glulam members as top and bottom flanges, 12.5 mm thick plywood panels as web, and 38 mm x140 mm dimension lumber as stiffeners. In regions where shear forces are excessive, thin steel sheathing concealed in the beam was used as reinforcement. Due to transportation constrains, beam splices using steel plates and glulam rivets were introduced.

The application of PWB shows the possibility of designing and building wood composite members to span a large distance with commercially available timber materials which can be easily transported to and built on site.

Introduction

As a conventional construction material, wood has the advantage of light-weight, easy- fabrication, low-cost, and good structural performance. Being one of the few renewable building materials, wood and wood based material is an environmental friendly building material. Its use is attracting much attention from stakeholders seeking “green” solutions in construction practice. Commercially available solid sawn timber has size limitations. Over the years, engineered wood products such as structural panel (plywood/OSB), glued laminated timber (Glulam), structural composite lumber, wood I beam, and wood trusses have been introduced in the market allowing large span structures to be built thus expanding the application of wood products in construction. This paper introduces the application of a built-up composite beam that can be assembled on site using commercially available material.

Besides structural safety issues, life cycle cost (LCC) of wood structures needs to consider functional, architectural and aesthetic effect which can be quantified by opportunity cost. As opportunity cost is unique for shear walls, it needs to be incorporated into probabilistic analysis of LCC analysis of wood frame structures. To perform probabilistic LCC analysis with the uncertainty from ground motion records and intensity measure, three methods have been implemented to solve the joint distribution of damage cost. The first method estimates damage cost from the summation of conditional distribution at given intensity measure. The second method estimates damage cost from the summation of conditional distribution of damage cost at given earthquake records. The third method implements Monte Carlo simulation to evaluate the probabilistic distribution of damage cost.

Introduction

Wood frame structures are generally recognized to provide good performance for collapse prevention and other structural safety requirements in earthquakes. However, severe damage loss of wood frame structures under moderate earthquakes, such as the 1994 Northridge Earthquake, has been reported. New design criteria in addition to the traditional failure control criteria are needed to reduce damage loss of wood frame structures in significant seismic events. LCC considers the costs over the structure’s lifetime, including construction cost, maintenance cost, damage cost, cost of loss of revenue, cost of injury and death, and discounting of cost over time [1, 2]. Optimized LCC helps decision makers balance initial construction costs and potential failure consequence. LCC oriented seismic design can provide a rational approach to evaluate damage cost for performance based design.

This paper reports the results of an experimental study to evaluate the contribution of self-tapping screws as perpendicular to grain reinforcements for bolted glulam connections with slotted in steel plates. Test results of beam-to-column connection specimens subjected to monotonic and reverse cyclic loading show that the connections reinforced with self-tapping screws have an increased capacity by a factor of 2 and 1.7 when compared to un-reinforced connections under monotonic and reverse cyclic loading, respectively. Retesting retrofitted failed un-reinforced connections with selftapping screw reinforcements also show increase in the capacity by 1.87 and 1.53 times compared to the un-reinforced case connections under monotonic and reverse cyclic loading, respectively. An extremely ductile failure mode was also observed with the reinforced connection.

Introduction

It is well known that bolted timber connections with slotted in steel plates have poor ductility and low moment resisting capacity. Due to their simplicity and elegance, designers commonly use these connections to transfer shear forces and ignore the contribution of their moment carrying resistance. When subject to loading such as seismic forces, the connection may experience bending moments not intended in the design, and the connection could fail prematurely because it may not be able to provide the needed moment resistance as they are governed by the tension perpendicular to grain and longitudinal shear strengths of timber: the two weakest strength properties of wood.