Performance-Based Earthquake Engineering - Coursework Example

 Part1 Furthermore, P and S are earthquake waves that travel with a speed that is reliant on density. Along with density, the speed of the seismic waves is also dependent on the elastic qualities of the soil and rocks because the waves go through the soil and rocks. The P waves due to their likeness with sonic boom are sensed first as they keep the capacity of banging and clattering windows. P waves are followed by S waves, which are more successful in destructing formations. The velocity of P waves can be found out by the subsequent equation: Vp = While the velocity of S waves can be found out as: Vs = k and μ in the above-mentioned equations are the volume modulus and rigidity, correspondingly, and density is symbolized as ρ. Surface wave is the third category of seismic wave. It is known as surface wave as its movement is constrained to the Earth’s surface. Surface waves are like the waves of the ocean as because of ocean waves, the water that is located at the distance downward to the ocean is not bothered. It is only bothered when the deep surface level raises and the displacement of soil and rocks near the depth lessens. Two kinds of surface waves can be found out. First kind that is named as love wave is similar to SH waves because of its movement that is being horizontally directional that is corresponding to the plane of the earth. It moves at the angles of ninety degree in relation to its point of transmission. Second kind that is named as Rayleigh wave is similar to ocean waves because of its vertical and horizontal movement due to which, the rock particles get relocated vertically in relation to direction of the movement of the waves (Bolt, 2004, p. 2.10). As shown by the arrows at the figure below, each point in the rock moves in an ellipse as the wave passes. Figure 1.5 Deformations produced by surface waves: (a) Rayleigh wave (vertical motion); (b) Love wave (horizontal motion). SOURCE: Engineering Seismology, by Bruce Bolt (2004, p. 2.10) The distinction between the different waves can be judged as: the surface waves in comparison to body waves move on a slow pace while the speed of love waves as compared to Rayleigh waves is at a faster pace. The difference in terms of slow and fast movement can be noticed in terms of the geographical development of these waves. Different kinds of waves travel in different directions because of their horizontal and vertical movements and get separated. However, because large earthquake sources are spatially extended faults, overlapping waves often obscure this separation of wave types. Love waves have no vertical ground component. Thus, because the seismograph component records only the vertical motion of the ground, the seismogram contains only P waves, vertically polarized S waves and Rayleigh waves. Figure 1.6 SOURCE: Engineering Seismology, by Bruce Bolt (2004, p. 2.10) Figure above shows a Seismograph from a magnitude 5.3 earthquake located 90 km away. The recording of the vertical component of ground motion clearly shows the separate onsets of the P and S waves. Time increases on the trace from left to right. As seismic waves move through layers of rock in the crust, they are reflected or refracted at the interfaces between rock types. As this happens, waves transform or evolve to other types. Bolt (2004) describes this action in a scientific manner: According to Bolt (2004), elasticity that is present between layers varies from one another and the waves get filtered by the help of these different layers that keep the capacity of amplification of waves at varied frequency rate. The waves are amplified and de-amplified by the help of these layers. At varied frequency rates, the resonance outcome is noticeable. After the arrival of P and S waves to the surface area, the energy that is created gets back to the crust due to which, the surface gets influenced concurrently because of horizontal and vertical movement of waves. Near the surface area, maximum trembling is felt because of enhanced amplification. The intensification of waves near earth’s surface increases the trembling destructiveness (p. 2.11). The earthquake waves show a tendency of moving in a revolving manner through rocks and soil. Due to this revolving motion, the structures face the danger of maximum damage as ground motion is extensive. While constructing buildings nowadays, the constructors keep in mind the revolving motion of the components of seismic waves. All categories of earthquake waves show themselves with moisture because of their contact with rocks and soil that have non-elastic qualities. For both S and P waves, frequency augments with attenuation rate of waves. Parameter Q is used for calculating seismic rate. For amplitude, A, for distance, d, for frequency A. f and for velocity c is used and following equation is used for calculating A: A= A0e(πfd/Qc) Part2 Using Pushover Analysis on a Church Building This section features a study of a basilica-type cathedral, which is evaluated using pushover analysis. Mele et al (2003, p. 355) used a two-step procedure comprising: (a) “3D static and dynamic linear analyses of the structural complex”. (b) “2D nonlinear push-over analysis of the single macro-elements”. The researchers also compared the results of the 3D linear analyses to the “macro-element ultimate strength capacity”. This provides an evaluation of the earthquake security intensity of the church. The competition that is done between demand and capacity substantiate the vulnerability of buildings like the church in terms of maximum destruction and fall down (Mele et al., 2003, p. 355). Church buildings are susceptible to heavy damage during earthquakes. Churches are more at stake due to earthquake because historically the churches are constructed with mechanical qualities in terms of construction material that are susceptible to damage such as building with low potency and nonlinear behaviour. Churches have structural systems that are not able to endure forces that are horizontally active and are generated because of earthquake. There is therefore the requirement of precise examinations on the effectiveness of conventional and ground-breaking retrofitting procedures, with the ambition of alternating a loom which grants the best equilibrium between the seismic protection needs and architectural protection viewpoint. Due to this fact, the colossal constructions are guaranteed of longer lives. It is therefore necessary to study the seismic behaviour of buildings, the vulnerable points, and to identify the parts or sections that may fail during earthquakes so that the different retrofit techniques should be applied. However, assessments of the structural behaviour have shown difficulties due to the following reasons: The analysis of the masonry materials needs multifarious notional form, and typically not uncomplicated to be put into practice in a restricted component (F.E.) model; The building materials that are used in church buildings are uncertain; the mechanical qualities of the building material indicate towards noteworthy distributions all through the construction, therefore the investigational characterization very frequently entails simplifications, which can give the wrong impression about the actual performance evaluation (Mele et al., 2003, pp. 355-356). As a result of these circumstances, Mele et al (2003) felt the requirement of particular modelling along with investigation approach for momentous churches. In evaluating the earthquake performance of church constructions, the above authors mentioned about the 1976 Friuli earthquake by the “GNDT” which is abbreviated as “Gruppo Nazionale per la Difesa dai Terremoti”. The research that was conducted was centred towards the evaluation and gathering of destruction and collapse patterns in the “macro-elements” of the church, and then they based their approach on the recognition, destruction pattern gathering and collapse evaluation of the solo macro-components in the church grouping. (Mele et al., 2003, p. 356) Another example is the fall down of the “San Francesco Church” in Assisi during the 1997. The church got collapsed because of the Umbro-Marchigiano earthquake which tells the need of studying the earthquake susceptibility of celebrated constructions and churches in order to preserve cultural heritage. A study was conducted on the S. “Ippolisto Martire Church”, located in Atripalda (Avellino, Italy) which was constructed from 1584 to 1612 on a prior cathedral of the fourth century AD. More innovations were introduced in the next centuries. In the year 1980, the Irpinia seismic activity hit the church and shattered some parts of it, which had been constructed after the destruction was there because of a prior earthquake. The structural typology featured the occurrence of very distinct construction typologies shaped by the grouping of relatively recurring construction designs or the supposed macro-components. Mele et al. (2003) argued that the examination of the fundamentals and the learning of the activities could provide elemental information on the worldwide presentation and helpful suggestions on the effectiveness of dissimilar re-establishment schemes. They then provided a procedure to be used in the difficult analysis method: (a) They analysed the overall structure in the linear array through an entire and sophisticated 3D model in order to characterize the static and dynamic performance, define the inner energy division between the uncomplicated fractions, and identify the weedy points of probable breakdown in the construction; (b) Out of the 3D context, single structural elements were extracted and analysed in the linear and nonlinear range through refined 2D models, in order to define the key construction qualities, which are different patterns of vibration and gaps, tangential potency capabilities, etc.; through this method assessment is simplified (Mele et al., 2003, p. 357). The strength of the nonlinear 2D model was compared with the forces performing on the 2D elements as copied from the stretchy division acquired in the 3D model. The contrast delivered a coarse approximation of the seismic protection intensity of the construction, and a suggestion of the kinds and sites for the necessary retrofit interferences (Mele et al., 2003, p. 357). In both of the static and dynamic evaluations, the models were focused to the perpendicular loads originating from the building materials’ own load and from the top weight, whereas in the static evaluations, the model was subjected to conformist static parallel behaviours functional at points equivalent to disseminated and protuberance loads. The dynamic analyses were approved with indication to the inelastic continuum offered by Eurocode 8, (cited in Mele et al., 2003, p. 358). The linear evaluations of the church provided information on the interface and the strain consequential division. The contrast of the consequences out of the evaluations identified the upshot of the forceful features of the construction on the interface between fundamentals and on the division of inner forces. The results acquired in the course of push-over evaluations were contrasted to the fall down loads copied from limit examination, and it demonstrated the capability of FEM nonlinear investigation to offer consistent replication of the authentic rejoinder of building material components. The potency requirement on every solo construction macro-component, consequential from the 3D linear evaluations, was contrasted to the macro-component eventual potency competence, approximated through 2D push-over evaluations. The contrasting requirement in relation to capacity entrenched that this category of construction is vulnerable to widespread breakage and fall down during earthquakes. The analysis defined an efficient two staged method for measuring the earthquake behaviour of building material for church constructions, comprising 3D static and dynamic linear evaluation of the construction components and 2D nonlinear push-over evaluations of the only macro-components. (Mele et al., 2003, p. 366) Mele (2003) and colleagues hoped the consequences extracted from the evaluations could be “extrapolated through parametric analyses carried out under appropriate hypotheses, to other significant cases and generalized for covering a wide building category” (p. 366). The static analyses subjected the model to traditional static parallel activities functional at points equivalent to disseminated and chunked loads. Subsequently two split load circumstances were noticed for the earthquake static evaluations, correspondingly with parallel actions implemented along the longitudinal course of the church building and by the side of the transversal route. The dynamic evaluations were also passed over in relation to the inelastic spectrum offered by Eurocode 8. The evaluation of the solo construction components and the study of their performances when contributing to the general reaction of the church building offered elementary information on the worldwide presentation and practical suggestions on the latent fall down patterns of the 3D structural complex. Part 3 Comparison of Pushover Design Method and Modal Analysis Method The pushover analysis method is used to evaluate the rate of betterment in terms of functionality because of usage of the devices that are created for this purpose. Devices are also employed for analyzing the appropriateness of different displacement based evaluation procedures that are used for measurement of earthquake retort. This is simple and economical in the assessment of buildings and structures. Elastic static analysis is the common currently employed design tool which is being supported by seismic codes. It has gained wide popularity because it offers the advantage of giving direct information on the magnitude and distribution of plastic strains within a structure based on the ground motions of buildings. Pushover method, also known as nonlinear static procedure, points towards an evaluation method which is performed in order to find a solution that is incremental as well as iterative for static equilibrium. The analysis uses a displacement-based design method, and employs simplified nonlinear techniques to quantify seismic behaviour. However, nonlinear history analysis requires a lot of computation. The simple method of analysis uses height of the constructed building along with the “static multimodal distribution” in place of “static uniform distribution” that is used for pushover evaluation explained by ATC-40 code (1996). The modal pushover analysis needs a sequence of pushover assessments, which have static “load distributions” that are analogous to the initial few forms of vibration. Both of the procedures use static elastic forms of vibration, however, in actuality, the forms of vibration transform incessantly when the structure is damaged or distorted because of lack of elasticity. For analyzing the incessant inelastic transformations, adaptive pushover methods are created due to which, “load pattern” transforms along with forms of vibration throughout deformation. These procedures though are computationally very costly. The study on pushover analysis of a church building allows this writer to have some knowledge on 2D and 3D static and dynamic linear assessments of the structural compound. Church buildings are testimonies to rich cultural heritage, and they are very susceptible to heavy damage during earthquakes. There is the necessity of precise examination on the effectiveness of conventional and ground-breaking retrofitting methods that should be applied on church buildings. On the other hand, the modal analysis method consists of a dynamic examination of a linear arithmetical replica of the construction in measuring the extreme “accelerations”, “forces” and “displacements”. This is based on structural dynamics theory, and then is enhanced to incorporate the involvements of every form of vibration that adds crucially to earthquake needs. Modal analysis leads to the responses history of the structure to a specified ground motion, but the method is usually in conjunction with a response spectrum. The internet can be used in disseminating vast information and knowledge on earthquakes and other natural disasters, and other valuable data in engineering principles so as to help engineers and aid workers cope with such natural calamities. The internet has helped create connection among people, has the capacity to boost the responsiveness of citizen networks, and has helped facilitate the exchange of information among states and citizens. Citizen networks, encouraged by the growth of the internet, will likely continue to grow and expand, becoming more powerful players on the international scene. (Kodrich & Laituri, 2005, p. 42) The internet and information technology have also helped engineers in designs of buildings. Part 4 As noted in the literature, earthquake motion has two components – horizontal and vertical. The horizontal movement is more considerable, but the effect of the vertical movement cannot be disregard especially for large span structures. Due to the recent progress in dynamic analysis techniques, and even with the exception of the statistical method the effect of the horizontal earthquakes motion on structures, has been checked in the actual design. The present design codes used in many countries of the world are: a) The seismic forces which act on the building shall be determined as the equivalent static loads using the statically evaluated seismic coefficients or the sheer force coefficients. The section of members shall be determined from the stresses and strains caused by these equivalent loads. b) The seismic forces which act on buildings shall be determined from the response spectrum, considering various factors such as the ground characteristics, natural periods and damping coefficients of buildings. Then the deflection and the story shear force can be calculated and the stresses and sections of each member determined. c) Considering subsoil conditions, earthquake motions shall be selected from past strong earthquake records and by means of structural response analysis of them; the sections shall be revised after considering the amount of deflection and the stresses. In the two last methods the intensity of the ground motion is given by the form of maximum acceleration. Although, some problems such as the energy dissipation between the ground and foundation, amplification factor of the ground, and the relationship, between the previously recorded ground motions and statistically expected ones still have no solution. So finally, it is really difficult to determine the earthquake motion which acts as the base of buildings. In the building Standard Law, the structures for which anti-seismic calculation is required, are as follows: (Building Standard Law, Chapter 6) 1. Buildings of more than 100 m2 in floor area used for schools, hospitals, clinics, theatres, cinema houses, market, public buildings, meeting halls, department stores, dormitories, and garages. 2. Wooden structures of more than 3 stories or 500m2 in floor area. 3. Any structure other than wooden structures which has more than two stores or 200 m2 in floor area. 4. Except those described in 1, 2, 3, the structures existing in the city-planned area or in the area designated by the governors of prefectures. In recent years numerous different dissipative systems have been proposed for improving the seismic performance of structures. There has been a swift addition in status due to estimated displacement-based procedures of earthquake plan, which are dependent on the utilization of non-linear static pushover evaluation. New ways to search their means into plan guides such as ATC 40 (1996), FEMA 356 (2000) AND ec8 (2003). Conventional “seismic design codes” for constructions endeavour at defensive measures for safety of human life by putting a stop to local or global fall down a sole intensity of earthquake (Fardis, 2009, p. 1). Fardis (2009) further claims that within a single-tier plan structure, improved security of services that are necessary or have huge possession is normally accomplished by amending the risk intensity of the “design seismic action”. The risks in relation to loss of possessions and belongings were identified in 1960s by the international earthquake engineering community and loss of lives caused by frequent seismic events was also identified. Fardis (2009) quotes these recommendations from the “Structural Engineers Association of California (SEAOC)” for seismic designs in 1968: “Structures should, in general, be able to: Resist a minor level of earthquake ground motion without damage. Resist a moderate level of earthquake ground motion without structural damage, but possibly experience some non-structural damage. Resist a major level of earthquake ground motion having an intensity equal to the strongest either experienced or forecast for the building site, without collapse but possibly with some structural as well as non-structural damage” (as cited in Fardis, 2009, p. 2) The SEAOC also formulated the “Performance-based earthquake engineering” from its SEAOC Vision 2000 document. After the formulation, the earthquake plan was designed by SEAOC, which came up as the most influential thought in many years (SEAOC 1995, cited in Fardis, p. 2). “Performance-based earthquake engineering” ventures to increase the usage by decreasing the total cost required for the completion of the work and the cost that is estimated in relation to coming damages pertaining to earthquakes. At present, this type of work is supported by restoring the conventional “single-tier seismic design” aligned with crumpling and its regulatory regulations, with an apparent “multi-tier seismic design”, gathering more than one detached “performance levels”, everyone under a varied earthquake incident, recognized with the help of its annual possibility of excessive and named “seismic hazard level”. The term “performance objective” is coined by engineers in performance-based earthquake engineering by considering the principles of “performance levels” and “seismic hazard levels”. (Fardis, 2009, p. 3) In 1972, engineers and architects, the Pacific Coast Building Officials Conference adopted the Uniform Building Code. The provisions required that the building should be designed for a lateral force applied at each floor and roof level as a constant percentage (7.5 to 10%) of the total dead plus live loads of the building above the plane (Bertero & Bozorgnia, 2004, p. 1-6). Read More