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CivE 490 Final Report EARTHQUAKE RESISTANT DESIGN Prepared for: Dr. R. Donahue Department of Civil & Environmental Engineering University of Alberta Prepared by: Joanna Chau ID# 294228 April 9, 2003 Executive Summary Many experimental studies have been carried out to examine different types of structural systems under the impact of earthquakes. These studies were all aimed toward the same goal, that is, to minimize the damages caused by the destructive power of earthquakes. The results from these studies demonstrated that for an earthquake resistant structure, it must have the following essential requirements: vertical bracing elements; horizontal elements, or diaphragm; and a continuous load path for the transmission of lateral forces to the ground. Some of the most common earthquake resistant structural systems include: shear wall dominant buildings, composite steel and concrete structural systems, masonry buildings, and steel buildings. The properties of earthquakes and the design of various types of earthquake resistant structural systems will be presented, along with recommendations to insure earthquake resistant performance of the structures. ii Table of Contents EXECUTIVE SUMMARY ................................................................................... II LIST OF FIGURES ......................................................................................... IV LIST OF TABLES ........................................................................................... V 1.0 INTRODUCTION ...................................................................................... 1 2.0 PROPERTIES OF EARTHQUAKES .............................................................. 1 2.1 Characteristics of Earthquake Ground Motion ...................................... 1 2.2 Behaviours of Building Structures During Earthquakes ........................ 2 3.0 EARTHQUAKE RESISTANT STRUCTURAL SYSTEMS.................................... 4 3.1 Shear Wall Dominant Buildings ............................................................ 4 3.2 Composite Steel and Concrete Structural Systems .............................. 7 3.2.1 Concrete-Filled Steel Tubes .................................................................. 8 3.2.2 Steel Reinforced Concrete .................................................................... 9 3.2.3 Composite Wall Systems..................................................................... 10 3.3 Masonry Buildings ............................................................................. 10 3.3.1 Confined Masonry ............................................................................... 11 3.3.2 Reinforced Masonry ............................................................................ 12 3.4 Steel Buildings ................................................................................... 15 3.4.1 Concentrically Braced Frames ............................................................ 15 3.4.2 Moment Resisting Frames .................................................................. 16 3.4.3 Eccentrically Braced Frames ............................................................... 17 4.0 CONCLUSIONS..................................................................................... 18 5.0 LIST OF REFERENCES .......................................................................... 19 iii List of Figures Figure 2.1. Seismic excitation of a building. ............................................................. 4 Figure 3.1. Tunnel form technique and construction system.................................... 5 Figure 3.2. Typical three-dimensional mesh modelling for tunnel form building structure. ................................................................................................. 6 Figure 3.3. Slab-wall interaction due to tension and compression (T/C) coupling. .. 7 Figure 3.4. Typical split-tee concrete-filled steel tube connection specimen. .......... 8 Figure 3.5. Construction of earthquake resistant traditional stone-masonry wall. . 11 Figure 3.6.1. Reinforced hollow unit masonry. .......................................................... 13 Figure 3.6.2. Reinforced grouted cavity masonry construction system..................... 13 Figure 3.6.3. Reinforced pocket type walls.. .............................................................. 13 Figure 3.7. Typical concentrically braced frame configurations. ............................ 16 iv List of Tables Table 2.1. Wave propagation velocities in various types of soil. ................................ 2 Table 3.1. Recommended maximum building height, H, and number of stories, n. . 14 v 1.0 Introduction Due to the destructive power of earthquakes, the safety and stability of buildings located in areas that are faced with extensive earthquake risks should be verified for seismic loads. Such verification is dependent on the results of geological and seismological studies, which provide data on the seismic activity of the location and recommend the values of parameters to be used in the evaluation of the expected seismic actions. However, verification is also based on the analysis of earthquake damage and mechanisms of collapse, as well as subsequent experimental investigations in the seismic behaviour, which give the starting point for the development of methods for structural verification of newly designed buildings (Tomaževič, 1999). In this report, the damages of structures due to earthquakes, and the design of earthquake resistant buildings will be analyzed. To get a better understanding of earthquake resistant design, the properties of earthquakes and some of the different types of earthquake resistant structural systems will be examined in detail. 2.0 Properties of Earthquakes 2.1 Characteristics of Earthquake Ground Motion The ground motion that is generated by sudden displacements within the earth’s crust is called an earthquake. Earthquakes are caused by various natural phenomena, such as volcanic eruption and fault rupture, which leads to seismic waves to propagate away from the causative fault and through the geological layers, and this wave propagation leads to oscillation of the ground (Tomaževič, 1999). The two types of seismic waves are called the longitudinal and transverse 1 waves. The longitudinal waves propagate in the same direction as the vibration and the transverse waves propagate in the direction that is perpendicular to the vibration. Since the propagation velocity of longitudinal waves is faster than that of transverse waves, therefore longitudinal waves are often called the primary waves (P-waves) and transverse waves are called the secondary waves (Swaves). Some typical values of the wave propagation velocities are shown in Table 2.1 (Tomaževič, 1999). The effects of earthquake ground motions on the behaviour and integrity of structures are dependent on the strength, frequency content, and duration of the ground oscillation (Gosh, 1991). Table 2.1. Wave propagation velocities in various types of soil. Taken from Tomaževič, 1999. 2.2 Behaviours of Building Structures During Earthquakes Selecting the appropriate load carrying system is an important parameter that will determine the performance of building structures under any loading. Especially in earthquake resistant design, since the intensity and orientation of loading are highly uncertain, therefore more emphasis must be placed upon selecting the proper type of structural systems. Buildings with simple, regular, and compact layouts that incorporate a continuous and redundant lateral force resisting system tend to perform fairly well and thus are desirable. Complex structural systems that may contain uncertainties in the analysis and detailing or that rely on non-redundant load paths can often cause unexpected and 2 potentially undesirable structural behaviour (Gosh, 1991). There are certain essential requirements for all earthquake resistant building structures. It is crucial for the structure to have adequate vertical bracing elements, either frames or shear walls, which provide stability to the structure by transferring all the earthquake forces to the ground. There must also be horizontal elements, or diaphragms, that tie the structure together and distribute all lateral forces to the vertical bracing elements. A continuous load path is necessary for the transmission of the lateral forces, from its point of origin to the ground (Green, 1987). Failing to provide adequate strength and toughness to each individual element in the system, or failing to tie all the individual elements together can cause distress or complete collapse of the system. During a seismic excitation, the deformation of a structure is due to the forced motion of its foundations, which will then produce oscillation of the structure (as illustrated in Figure 2.1). In this process, a certain amount of kinetic energy will be imparted to the structure in the form of elastic deformation. This energy, during the consecutive phases of structure oscillation, will alternate continuously from kinetic to potential energy and vice versa, until it is dissipated in the form of the heat through the process of viscous and hysteretic damping (Penelis and Kappos, 1997). As a result, the main concern for the structural engineers when designing an earthquake resistant structure is to construct a structural system that is able to dissipate this kinetic energy through successive deformation cycles, without exceeding certain damage limits, defined for characteristic excitation levels (Penelis and Kappos, 1997). 3 Figure 2.1. Seismic excitation of a building. Taken from Penelis and Kappos, 1997. 3.0 Earthquake Resistant Structural Systems 3.1 Shear Wall Dominant Buildings Shear wall dominant multi-storey reinforced concrete structures, constructed using tunnel form techniques are often used in countries that encounter extensive seismic risk such as Japan, Turkey and Chile (Balkaya and Kalkan, 2003). Shear wall dominant buildings are composed of vertical and horizontal panels set at right angles and are supported by struts and props. Figure 3.1 is a typical illustration for this type of unique structure. There are no beams or columns used and these structures generally use all wall elements as the primary load carrying members. With this type of construction technique, the use of precast load carrying members is avoided (Balkaya and Kalkan, 2003). The shear walls will act as vertical cantilever beams, which transfer lateral forces from the superstructure to the foundation. Most of the shear wall dominant structures contain a number of walls which resist lateral load in two orthogonal directions. (Canadian Prestressed Concrete Institute, 1996). The walls and slabs, having almost the same thickness are cast-in-place in one single operation. Thus, it reduces the number of joints required for the members and 4 allows the casting of walls and slabs to be completed at a very rapid speed. This simultaneous casting of walls, slabs and cross-walls results in monolithic structures, which provides high seismic performance and, as a result, allowing them to meet the seismic code requirements of many countries that are located in regions facing great earthquake risks. In addition to their considerable earthquake resistance, the simplicity and speed of building make them preferable as the multi-unit construction of public and residential buildings (Balkaya and Kalkan, 2003). Figure 3.1. Tunnel form technique and construction system. Taken from Balkaya and Kalkan, 2003. In 1999, two severe urban earthquakes struck the Kocaeli and Düzce provinces in Turkey with magnitudes (Mw) of 7.4 and 7.1. These disasters caused substantial structural damage and casualties. In the outcome of these disastrous earthquakes, no damages or demolished shear wall dominant buildings constructed using the tunnel form techniques were reported. The nearly non-damaged conditions of these unique structures drew people’s attention to focus on their dynamic properties (Balkaya and Kalkan, 2003). 5 Another major requirement of an earthquake resistant structure is the ability to respond to strong motion by progressively mobilizing the energy dissipative capacities of an ascending hierarchy of elements making up the structure. In these shear wall dominant multi-storey structures, when the shear walls are designed properly, it can become economical and effective lateral stiffening elements, which can be used to minimize potentially damaging interstorey drifts in multi-storey structures during earthquake excitations (Balkaya and Kalkan, 2003). As mentioned before, for these structures, the shear walls and slabs have almost the same thickness, less than those of standard building slabs. Therefore, diaphragm flexibility can greatly reduce the dynamic behaviour. The transverse walls, which are perpendicular to the main walls and the loading direction, provide additional resistance and increase the predicated load capacity considerably due to the tension/compression (T/C) coupling effect (Figure 3.3) produced by the in-plane or membrane forces in the walls (Balkaya and Kalkan, 2003). Figure 3.2. Typical three-dimensional mesh modelling for tunnel form building structure. Taken from Balkaya and Kalkan, 2003. 6 Figure 3.3. Slab-wall interaction due to tension and compression (T/C) coupling. Taken from Balkaya and Kalkan, 2003. However, one observed drawback of this type of building structure is their torsional behaviour, it is an exceptionally important criteria in the dynamic mode of those structures that should be taken into account for the design. Since part of the outside walls should be opened in order to take the formwork back after the casting process, therefore, the buildings may behave like thin-wall-tubular structures where the torsional rigidity is low. In addition, rectangular plans tend to have weaker bending capacity along their short sides than that of square plans due to their architectural and constructional limitations (Balkaya and Kalkan, 2003). As a result, the designer should pay special attention to these details. 3.2 Composite Steel and Concrete Structural Systems The use of composite steel and concrete structural systems as the primary lateral resistance systems in building structures subjected to seismic loading can provide significant advantages. While composite construction has been common for over half a century through the use of composite beam and joist floor systems, over the past decade, a substantial amount of research has been conducted worldwide on a wide range of composite lateral resistance systems. These systems include unbraced moment frames consisting of steel girders with concrete-filled steel tube (CFT) or steel reinforced concrete (SRC) 7 beam-columns; braced frames having concrete-filled steel tube columns; and a variety of composite wall systems (Hajjar, 2001). 3.2.1 Concrete-Filled Steel Tubes Concrete-filled steel tube columns are commonly used in building construction as the super-columns in high-rise structures, where they form the primary load bearing members in the building’s gravity and lateral resistance systems (Hajjar, 2001). But recently, many building contractors and researchers have started to realize the potential economic benefits of using composite concrete-filled steel tube frames, consisting of steel I-girders framing into circular, square, or rectangular concrete-filled steel tubes using fully-restrained or partially restrained connections for unbraced frames, or using pin connections for braced frames. Concrete-filled steel tube structural members have a number of distinct advantages when comparing to the steel, reinforced concrete, or steel-reinforced concrete members. The steel that lies at the outer perimeter can efficiently resist flexure, axial tension, and compression, while the concrete in the inside forms an excellent core to facilitate the resistance of compressive loading. Therefore, longitudinal reinforcing bars are not necessary along the length of the concretefilled steel tube (Hajjar, 2001). Figure 3.4. Typical split-tee concrete-filled steel tube connection specimen. Taken from Hajjar, 2002. 8 In construction, the tube itself can act as the formwork, and their erection can precede the concrete by several stories, which can reduce both the labour and material costs. When using composite concrete-filled steel tube frames, the concrete-filled steel tubes give excellent monotonic and seismic resistance in two orthogonal directions and can withstand biaxial bending and axial compression. In lateral system design, the use of concrete-filled steel tubes as part of the moment resisting frames can yield a high strength-to-weight ratio due to confinement of the concrete and continuous bracing of the steel tube to delay local buckling, improved damping behaviour in comparison to the traditional steel frames, and enhanced ductility and toughness. In the event of earthquake excitation, the cyclic response of concrete-filled steel tubes and their connections provides full hysteresis loops with substantial energy dissipation (Hajjar, 2001). 3.2.2 Steel Reinforced Concrete Steel reinforced concrete beam-columns have the ability to yield high strength and ductility relative to the reinforced concrete members. Above the concrete pour, the encased steel section is often erected for several stories, thus, allowing the steel girders to be framed into the steel columns, which will then facilitates ongoing construction of the remainder of the steel structure. Similar to concrete-filled steel tubes, longitudinal reinforcement in the columns is not necessary (Hajjar, 2001). Comparing the steel reinforced concrete to reinforced concrete, when these two types of concrete beam-columns are subjected to axial force plus cyclic shear, placing the member into double curvature, as would be exhibited by a beam-column in a moment resisting frame structure, the steel reinforced concrete beam-columns show very good response, with improved ductility over the corresponding reinforced concrete member (Hajjar, 2001). 9 3.2.3 Composite Wall Systems The composite wall systems can act as great lateral resistance systems in areas ranging from lowto high seismicity. The advantages of using composite wall systems include: Ease of construction through the use of ductile wall system details, which can prevent the overcrowding of reinforcing bars than in reinforced concrete, together with gravity steel framing throughout the rest of the building; Ability to use the walls as architectural partitions in a variety of configurations compared to the conventional steel braced frames for example; High initial stiffness to help eliminate drift; Good damping characteristics; and Easier to repair after moderate damage by using epoxy on the cracked walls (Hajjar, 2001). 3.3 Masonry Buildings Masonry buildings are box-type structural systems composed of vertical and horizontal structural elements, walls and floors, connected in every direction. Horizontal connecting elements, steel ties or reinforced-concrete bond-beams (tie-beams) are provided at floor levels to connect the walls. During earthquakes, floors should act as rigid horizontal diaphragm, which allows the seismic inertia forces be distributed among the structural walls in proportion to their stiffnesses. Any type of floors may be used, given that the general requirements of continuity and effective diaphragm action are satisfied. Masonry exists in the form of 10 confined, un-confined, reinforced, un-reinforced masonry (Tomaževič, 1999.). Confined, reinforced masonry will be discussed in more details. Figure 3.5. Construction of earthquake resistant traditional stone-masonry wall. Taken from Tomaževič, 1999. 3.3.1 Confined Masonry Confined masonry is a construction system where masonry structural walls are confined on all four sides with reinforced concrete or reinforced masonry vertical and horizontal confining elements, which are not intended to carry vertical and/or horizontal loads, as a result, it is not designed to perform as a moment-resisting frames (Tomaževič, 1999.). But for confined masonry walls, they are intended to carry all vertical and seismic loading. As shown by experimental results and past experiences obtained after earthquakes, confining the masonry walls with bond-systems and tie-columns can provide the following: Improvement in the connection between structural walls; Improvement in the stability of slender structural walls; Improvement in strength and ductility of masonry panels; and Reduction in the risk of disintegration of masonry panels damaged by the earthquake. 11 In order to ensure structural integrity, vertical confining elements should be situated at all corners and recesses of the building, also at all joints and wall intersections (Tomaževič, 1999.). The results obtained from experimental investigations of subjecting single storey masonry houses to dynamically imposed sinusoidal displacements with increasing amplitudes, it demonstrated that vertical tie-columns can improve the ductility of masonry buildings significantly, while only causing small impact on the lateral resistance. Similar results have been demonstrated by the static cyclic tests. By conducting correlation studies that compare the behaviour of plain masonry wall panels, which often shows relatively poor masonry quality, to confined masonry, the results obtained clearly suggests that the confined masonry elements can improve the seismic behaviour (Tomaževič, 1999.). Recently, energy dissipation capacity and ductility of masonry wall assemblages, confined and reinforced in different ways, as well as the influence of horizontal reinforcement on the seismic behaviour, have been experimentally investigated. These conclusions all suggests that confinement can improve the lateral resistance and energy dissipation capacity of a masonry wall (Tomaževič, 1999.). 3.3.2 Reinforced Masonry Reinforced masonry is a construction system, where steel reinforcement in the form of reinforcing bars or mesh is embedded in the mortar or placed in the holes and filled with concrete or gout (Tomaževič, 1999.). By reinforcing the masonry with steel reinforcement, the resistance to seismic loads and energy dissipation capacity may be improved considerably. To achieve this, the reinforcement should be integrated with masonry so that all materials of the reinforced masonry system act monolithically when resisting gravity and seismic 12 loading (Tomaževič, 1999.). There are many ways in which steel reinforcement can be used in a reinforced masonry structural system. The three basic types of reinforced masonry systems are: reinforced hollow unit masonry (Figure 3.6.1), reinforced grouted cavity masonry (Figure 3.6.2), and reinforced pocket type walls (Figure 3.6.3). Figure 3.6.1. Reinforced hollow unit masonry. Taken from Tomaževič, 1999. Figure 3.6.2. Reinforced grouted cavity masonry construction system. Taken from Tomaževič, 1999. Figure 3.6.3. Reinforced pocket type walls. Taken from Tomaževič, 1999. During shear failure, plain masonry walls behave as brittle structural elements with limited energy dissipation capacity, especially when subjected to high compression stresses. To improve lateral resistance and ductility of the 13 masonry walls, the walls can be reinforced with steel reinforcement, which is placed either in the joints between the units and embedded in the mortar, or in specially provided holes and channels within the units and grouted with concrete or grout. If a masonry wall is reinforced horizontally, the reinforcement will prevent the separation of the cracked part of the wall at shear failure, thus improving the resistance and energy dissipation capacity of the wall when subjected to repeated lateral load reversals (Tomaževič, 1999.). But for un- reinforced masonry walls, even a single diagonal crack may cause severe deterioration in strength and followed by brittle collapse. Conversely, if the walls are reinforced horizontally, many cracks, evenly distributed over the entire surface of the walls, may develop before causing the wall to collapse. At ultimate state, crushing of masonry units due to bending plus shear is often observed, indicating that the load bearing capacity of masonry units is fully utilized (Tomaževič, 1999.). Even though the seismic resistance of all masonry buildings should be verified by calculation, it is recommended that, knowing the available quality of masonry materials and technology, the height and number of stories of masonry buildings constructed in one of the construction systems may not exceed the recommended values (Tomaževič, 1999.) specified in Table 3.1. Table 3.1. Recommended maximum building height, H, and number of stories, n. Taken from Tomaževič, 1999. 14 3.4 Steel Buildings All buildings must have a structural system that is capable of resisting lateral loads due to earthquakes. Some of the common vertical lateral vertical load resisting systems in steel framed buildings include concentrically braced frames, moment resisting frames, and eccentrically braced frames. Alternatively, steel plate shear walls, base isolation techniques, and energy absorbing elements in braced frames are also used (Medhekar and Kennedy, 1997). 3.4.1 Concentrically Braced Frames Concentrically braced frames are vertical cantilever trusses that are commonly used in low-rise buildings. Typical configurations of these concentrically braced frames are shown in Figure 3.7. They are appropriate in situations with low to moderate ductility demand (Medhekar and Kennedy, 1997). Concentrically braced frames have simple beam-to-column connections. Lateral stiffness and strength are provided by the diagonal braces, which are attached concentrically to the beam-to-column connection using gusset plates. Energy dissipation is imparted by the ability of the braces to yield in tension. The braces may also be designed to buckle in-elastically in compression (Medhekar and Kennedy, 1997). Concentrically braced frames are economical due to the relative ease in design, detailing, and construction. They are also very efficient since the members are primarily subjected to axial loads. Concentrically braced frames are stiff systems that provide good control of lateral drift, thus minimizing damages to the non-structural components. Damaged brace members can be replaced relatively easily as well (Medhekar and Kennedy, 1997). However, due to its low redundancy, this system is not preferred in areas that are subjected to high earthquake risks. The absence of alternative load paths may cause severe 15 consequences when the components fail. The ability to resist compressive forces of the diagonal braces tends to degrade under cyclic loading; as a result, the frames may deteriorate in strength and stiffness considerably. Frames that rely only on the tension diagonal to resist lateral force may have components subjected to impact loads due to the slackness developed in the diagonals (Medhekar and Kennedy, 1997). Figure 3.7. Typical concentrically braced frame configurations. Taken from Medhekar and Kennedy, 1997. 3.4.2 Moment Resisting Frames Moment resisting frames have beam-to-column connections that are capable of transferring moment. The moment resisting frames are also more ductile than concentrically braced frames (Medhekar and Kennedy, 1997). Energy dissipation takes place by flexural yielding in the plastic hinges, which are formed at the ends of the members. This system creates no obstruction between the columns and thus provides maximum freedom in the interior planning and fenestration (Medhekar and Kennedy, 1997). It is also highly redundant. Consequently, it is preferred in areas that are faced with high earthquake risks. However, since it is a rather flexible system, adequate drift control may not be 16 provided. Subsequently, non-structural components of the system may be damaged in moderate events (Medhekar and Kennedy, 1997). In addition, the frame design is usually governed by stiffness considerations rather than by the strength of the individual members. This leads to the evolution of dual systems comprising both the concentrically braced frames and moment resisting frames. The former can provide drift control in moderate but frequent events, while the latter provides the ductility required to survive in case of an extreme event (Medhekar and Kennedy, 1997). Engineers usually design these moment resisting frames with either full-strength rigid joints or simple pinned joints, but recent experimental investigations show that some alternative connection types, such as flush end-plate connection joints and improved welded moment connections, may be used to enhance the ductility of these connections. The flush end-plate connection joints allow plastic deformation of the frames to be in control by determining the ductility capacity of the connection joints in advance. Thus, allowing the frames to behave in a satisfactory predetermined manner (Thomson and Broderick, 2002). 3.4.3 Eccentrically Braced Frames Eccentrically braced frames consist the advantages of both the concentrically braced frames and moment resisting frames. They have beam-tocolumn connections that are capable of transferring moments. In addition, the braces provided have at least one eccentric connection. In these braces, the force is transferred through a “link” element to the beam-to-column connection. For eccentrically braced frames, energy dissipation takes place in the “link” element by shear or flexural yielding. The braces are also designed to remain elastic and not to buckle (Medhekar and Kennedy, 1997). 17 4.0 Conclusions During a seismic excitation, the deformation and oscillation of structures are due to the forced motion of its foundation. A certain amount of kinetic will be imparted to the structure during this process, therefore, for any earthquake resistant building, it must be able to dissipate this kinetic energy. Moreover, the earthquake resistant building must have adequate vertical bracing elements, horizontal elements, and a continuous load path for the transmission of lateral forces to the ground. Some of the commonly found earthquake resistant structural systems include: shear wall dominant buildings, composite steel and concrete structural systems, masonry buildings and steel buildings. Shear wall dominant buildings are constructed using the tunnel form techniques, which are often used in countries that encounter substantial seismic risk. Composite steel and concrete structural systems are used quite extensively as the primary lateral resistance system in buildings. These systems include unbraced moment frames consisting of steel girders with concrete-filled steel tube or steel reinforced concrete beamcolumns, braced frames having concrete-filled tube columns, and a variety of composite wall systems. Masonry may take the form of confined, un-confined, reinforced, and un-reinforced masonry. Typical vertical lateral load resisting systems in steel framed buildings include concentrically braced frames, moment resisting frames, and eccentrically braced frames. 18 5.0 List of References Balkaya, C., and Kalkan, E. 2003. Estimation of Fundamental Periods of ShearWall Dominant Building Structures. Earthquake Engineering and Structural Dynamics, 32:985-998. Canadian Prestressed Concrete Institute. 1996. Precast and Prestressed Concrete Design Manual, 3rd Ed. Ottawa, ON. Ghosh, S.K. 1991 Earthquake-Resistant Concrete Structures Inelastic Response and Design. American Concrete Institute, Detroit, Michigan. Green, N.B. 1987. Earthquake Resistant Building Design and Construction, 3rd Ed. Elsevier Science Publishing Co., Inc., New York. Hajjar, J.F. 2002. Composite Steel and Concrete Structural Systems for Seismic Engineering. Journal of Constructional Steel Research, 58:703-723. Medhekar, M.S., and Kennedy, D.L. 1997. Seismic Evaluation of Steel Buildings with Concentrically Braced Frames. Structural Engineering Report 219, Department of Civil and Environmental Engineering, The University of Alberta, Edmonton, Alberta. Penelis, G.G., and Kappos, A.J. 1997. Earthquake-Resistant Concrete Structures. E & FN Spon, London. 19 Ricles, J.M., Fisher, J.W., Lu, L., and Kaufmann, E.J. 2001. Development of Improved Welded Moment Connections for Earthquake-Resistant Design. Journal of Constructional Steel Research, 58:565-604. Thomson, A.W., and Broderick, B.M. 2002. Earthquake Resistance of Flush End-Plate Steel Joints for Moment Frames. Proceedings of the Institution of Civil Engineers, Trinity College, Dublin. Tomaževič, M. 1999. Earthquake-Resistant Design of Masonry Buildings. Imperial College Press, London. 20