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<p>I n d o n e s i a</p>
<p>Seismic Resistance Design Standard for Buildings (Standar Perencanaan Ketahanan Gempa Untuk Struktur Bangunan Gedung) or SNI02-1726-2002. 2002 Indonesian National Standarization Agency; Ministry of Public WorkEditorial Note: According to the information provided by the national delegate, the code had been changed in 2002 and enhanced in 2002. The code will be changed in 2009. They are written in Indonesian.</p>
<p>25-1</p>
<p>Comments on Building Codes 1. General a. Name of Country: INDONESIA b. Name of Codes: Seismic Resistance Design Standard for Buildings (Standar Perencanaan Ketahanan Gempa Untuk Struktur Bangunan Gedung) or SNI02-1726-2002. c. Issued by: Indonesian National Standarization Agency; Ministry of Public Work d. Enforcement Year: 2002 2. Structural Design Method a. Format: (please check) Working Stress Design : Allowable Stress Actual Stress Ultimate Strength Design: Ultimate Member Strength Required Member Strength Limit State Design : Ultimate Lateral Strength Required Lateral Strength Other Design Method : (comment) The structural design method in SNI02-1726-2002 is similar to the design method in many international building codes, such as IBC 2000. b. Material Strength (Concrete and Steel): The ultimate strength of materials is used in the ultimate strength design. c. Strength Reduction Factors: Ru = Rn Where Ru is the ultimate strength, Rn is the nominal strengh, and is the strength reduction factor. The combination of strength reduction factor and the load factor should be such that a level of confidence of minimum = 3 for load combination of dead load and live load, and minimum = 2 for lod combination of dead load, live load, and earthquake load, can be achieved. d. Load Factors for Gravity Loadings and Load Combination: For load combination with dead load and live load : Qu = D Dn + L Ln For load combination with dead load, live load and earthquake: Qu = D Dn + L Ln + E En where D, L dan E are the load factors for nominal dead load, nominal live load, and nominal earthquake load, respectively, which values are determined on the standard of building loads, and/or standard of materials. e. Typical Live Load Values: Office Buildings : 2.5 kN/m2 Residential Buildings: 2.0 kN/m2 f. Special Aspects of Structural Design Method The seismic provisions of the building code utilize a Design Basis Earthquake that should be used in the structural analysis. The provisions allow buildings to be designed to resist the design basis earthquake such that the structures can have damage on structural elements while preventing total collapse. Design Basis Earthquake is based on a probability approach with 10 percent of probability of exceedence in 50 years, or equivalent with a return period of 475 year. </p>
<p>25-2</p>
<p>SEISMIC RESISTANT DESIGN STANDARD FOR BUILDING STRUCTURES SNI17262002By : Wiratman WangsadinataEmeritus Professor, Tarumanagara University President Director, Wiratman & Associates Chairman SNI-1726-2002 Committee</p>
<p>ABSTRACTIn this summary paper, the main principles of the Indonesian Seismic Resistant Design Standard for Building Structures SNI-1726-2002 are explained. The summary covers seismic design provisions on basic requirements for building design and material strengths. The Design Earthquake considered has a return period of 500 years (10 % probability of exceedance in 50 years) and the resulting peak base rock acceleration forms the basis for establishing the Indonesian Seismic Zoning Map. The peak ground acceleration depends on the soil category (site-class) present on top of the base rock. With this acceleration the response spectra of the Design Earthquake are defined for determining the effect of the Design Earthquake upon building structures. Under the effect of the Design Earthquake the building structure is at its state of near collapse with a maximum deflection, assumed to be the same for any ductility level of the structure. With this assumption and known overstrength in the structure, for a certain level of ductility, a simple formulation is established regarding the effect of the Design Earthquake upon a building structure, such as elastic load, maximum load on the structure at its state of near collapse, first yield load and nominal load for design. Against the effect of the Design Earthquake, a building structure is in general analysed dynamically using response spectrum modal analysis method. However, regular building structures, having their first and second mode motion dominantly in translation, may be analysed statically using equivalent static seismic loads. The substructure (basement and foundation) may be analysed as a separate structure subjected to the effect of the Design Earthquake originating from the superstructure, from own inertial forces and from the surrounding soil. Finally the strength design of the substructure based on the Load and Resistance Factor Design method is discussed.</p>
<p>Key words: Standard, earthquake, dynamic response, structure, building, ductility. 1. INTRODUCTION</p>
<p>This standard has taken into account as far as possible the latest development of earthquake engineering in the world, particularly what has been reported by the National Earthquake Hazards Reduction Program (NEHRP), USA, in its report titled NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures (February 1998), but on the other hand maintains as close as possible the format of the previous Indonesian standard Rules for Earthquake Resistant Design of Houses and Buildings (SNI 03-1726-1989). In general this standard is sufficient to be used as the basis for the modern design of seismic resistant building structures, particularly highrise buildings. In order that the building engineering community understands what the basic principles are of this standard, in this paper their background are explained. More detailed explanations can be found in the commentary of the respective clauses, which is an integral part of the standard. 2. DESIGN EARTHQUAKE AND SEISMIC ZONING MAP OF</p>
<p>25-3</p>
<p>INDONESIA An earthquake is a natural phenomena in the form of local ground motion generated by tectonic movements of the earths crust, its occurrence being probabilistic. This means that if a certain period of time is considered, the probability of occurrence of mild earthquakes is higher than of large earthquakes during that period. In other words, mild earthquakes have a relatively short return period, while strong earthquakes a relatively long one. For the seismic resistant design of building structures, according to this standard a Design Earthquake causing local ground motion with a return period of 500 years must be considered. According to the probability theorem, approximately such an earthquake has a probability of exceedance of 10% in a period of 50 years. This period of 50 years is assumed to be the life time of normal buildings with no particular importance. The local ground motion as the basis for the seismic resistant design of building structures, is generally expressed in the peak ground acceleration. This motion is the result of seismic waves propagating from the base rock located below the surface. While propagating, the waves undergo amplifications. The softer the soil layers are on top of the base rock, the greater the amplification. Conversely, the harder the soil layers are on top of the base rock, the smaller the amplification. To determine the local ground motion with a return period of 500 years caused by the Design Earthquake, a probabilistic seismic hazard analysis must be conducted. From the result of such an analysis peak base accelerations with a return period of 500 years at numerous locations throughout Indonesia have been obtained. Thus, on the map of Indonesia contour lines, showing points with equal peak base acceleration with a return period of 500 years, have been drawn. Based on such a contour line map, the Seismic Zoning Map of Indonesia has been established as shown in Figure 1. The seismotectonic input data for the probabilistic seismic hazard analysis consist of: earthquake source areas; magnitude frequency distribution at the earthquake source areas; attenuation function, relating local peak base acceleration, earthquake magnitude at the focus and distance from the focus to the site; minimum and maximum magnitude at the source areas; annual frequency of occurrence of earthquakes of any magnitude at the source areas; and the mathematical model of the earthquake occurrence itself. For the earthquake source areas, all foci recorded in the seismic history of Indonesia have been considered, including foci at subduction zones, shallow crustal foci within tectonic plates and foci on active faults so far identified. The magnitude-frequency distribution at the earthquake source areas has been computed based on the available statistical seismic data. This distribution is better known as the Gutenberg-Richter and exponential magnitudefrequency recurrence function. For the attenuation functions, several ones have been considered, namely the ones proposed by Fukushima & Tanaka (1990), Youngs (1997), Joyner & Boore (1997) and Crouse (1991). Earthquake occurrence has been mathematically modelled following Poissons function. In this probabilistic seismic hazard analysis, peak base accelerations and their return periods have been obtained through successive computations of the following items: (1) total probability by considering all possible earthquake magnitudes and distances to the foci (the double integral after</p>
<p>25-4</p>
<p>0 80</p>
<p>200</p>
<p>400</p>
<p>10O N</p>
<p>Kilometer</p>
<p>5O N</p>
<p>0O</p>
<p>I ND</p>
<p>5O S</p>
<p>A</p>
<p>I</p>
<p>N O</p>
<p>C</p>
<p>E</p>
<p>A</p>
<p>N</p>
<p>10OS</p>
<p>1 415OSO</p>
<p>0.03 g 0.20 g100O</p>
<p>2 5</p>
<p>0.10 g 0.25 g105O</p>
<p>3 6</p>
<p>0.15 g 0.30 g110 O 115 O 120O 125O 130O 135O 140O</p>
<p>Figure 1.</p>
<p>095</p>
<p>The Seismic Zoning Map of Indonesia with peak base acceleration with a return period of 500 years.</p>
<p>Cornell, 1968), (2) the annual total probability, (3) the annual event probability (Poissons function), (4) the return period (which is the inverse of the annual probability), and (5) the peak base accelerations with a mean return period of 500 years, obtained through interpolation (logarithmic). On the Seismic Zoning Map of Indonesia (Figure 1) it can be seen, that Indonesia is divided into 6 seismic zones, Seismic Zone 1 being the least and Seismic Zone 6 the most severe seismic zone. The mean peak base acceleration for each zone starting from Seismic Zone 1 to 6 are respectively as follows : 0.03 g, 0.10 g, 0.15 g, 0.20 g, 0.25 g and 0.30 g (see Figure 1 and Table 2). It should be noted, that the peak base acceleration for Seismic Zone 1 is the minimum value to be considered in the design of building structures, to provide a minimum robustness to the structure. Therefore, this peak base acceleration has a rather longer return period than 500 years (conservative). 3. LOCAL SOIL CATEGORY AND PEAK GROUND ACCELERATION</p>
<p>From the previous discussion it follows, that the peak ground acceleration may be obtained from the result of a seismic wave propagation analysis, whereby the waves are propagating from the base rock to the ground surface. However, this standard provides conveniently the value of the peak ground acceleration for every seismic zone for 3 categories of soil present on top of the base rock, namely Hard Soil, Medium Soil and Soft Soil. According to this standard, the differentiation of the soil category is defined by the following 3 parameters : shear wave velocity vs, Standard Penetration Test (SPT) or N-value and undrained shear strength (Su). The base rock for example is defined as the soil layer below the ground surface having shear wave velocities reaching 750</p>
<p>25-5</p>
<p>m/sec, with no other deeper layers having lower shear wave velocity values. According to another definition, the base rock is the soil layer below the ground surface having Standard Penetration Test values of at least 60, with no other deeper layers having lower N-values. The soil on top of the base rock generally consists of several layers, each with different values of the soil parameters. Therefore, to determine the category of the soil, the weighted average of the soil parameter must be computed using the thickness of each soil layer as the weighing factor. The weighted average shear wave velocity s , Standard Penetration Test value N and undrained shear strength S u , can be computed from the following equations :</p>
<p>vs =</p>
<p>i =1</p>
<p>m</p>
<p>ti .. (1)</p>
<p>i =1</p>
<p>m</p>
<p>t i / v sim</p>
<p>N =</p>
<p>i =1</p>
<p>ti .. (2)</p>
<p>i =1</p>
<p>m</p>
<p>t i / Nim</p>
<p>Su =</p>
<p>i =1</p>
<p>ti ..... (3)</p>
<p>i =1</p>
<p>m</p>
<p>t i / S ui</p>
<p>where ti is the thickness of layer i, vsi the shear wave velocity of layer i, Ni the Standard Penetration Test value of layer i, Sui the undrained shear strength of layer i and m is the number of soil layers present in the considered soil. Due to the fact that the amplification of waves propagating from the base rock to the gound surface is determined only by the soil parameters up to a certain depth from the ground surface, in using eqs.(1), (2) and (3) the total depth of the considered soil must not be taken more than 30 m. To consider soil depths of more than this is not allowed, as the weighted average of the soil strength tends to increase with depth, whereas soil layers below 30 m do not contribute in amplifying the waves. So, using the weighted average of soil parameters according to eqs.(1), (2) and (3) for a total depth of not more than 30 m, the definition of Hard Soil, Medium Soil and Soft Soil is shown in Table 1. In Table 1, PI is the plasticity index and wn the natural water content. Furthermore, what is meant by Special Soils are soils having high liquefaction potentials, very sensitive clays, soft clays with a total thickness of 3 m or more, loosely cemented sands, peat, soils containing organic materials with a thickness of more than 3 m, and very soft clays with a plasticity index of more than 75 and a thickness of more than 30 m. For these Special Soils the peak ground acceleration must be obtained from the result of a seismic wave propagation analysis. For the soil categories defined in Table 1, the peak ground acceleration Ao for each seismic zone is shown in Table 2.</p>
<p>25-6</p>
<p>Table 1. Soil CategoriesAverage shear wave velocity s (m/sec) Average Standard Penetration Average undrained shear strength S u (kPa)</p>
<p>Soil Category Hard Soil Medium Soil</p>
<p>N N > 5015 < N < 50</p>
<p>s > 350175 < s < 350</p>
<p>S u > 10050 < S u < 100</p>
<p>s < 175Soft Soil Special Soil</p>
<p>N < 15</p>
<p>S u < 50</p>
<p>Or, any soil profile with more than 3m of soft clays with PI > 20, wn > 40% and Su < 25 kPa. Site specific evaluation required.</p>
<p>Table 2.Seismic Zone 1 2 3 4 5 6</p>
<p>Peak Base Acceleration and Peak Ground Acceleration AoPeak Ground Acceleration Ao (g) Hard Soil 0.04 0.12 0.18 0.24 0.28 0.33 Medium Soil 0.05 0.15 0.23 0.28 0.32 0.36 Soft Soil 0.08 0.20 0.30 0.34 0...</p>