Bangladesh National Building Code 1993 Pdf Free Download

Bangladesh lies well within an active seismic zone and is prone to earthquakes. To determine earthquake forces on a structure, static analysis has gained popularity in the country and also in many other countries because of the simplicity of the method. This calls for the use of an established and tested building code so as to ensure the safety of the structure and its occupants against the natural hazard. Bangladesh National Building Code (BNBC) was first organized in the year of 1993 to fulfill the purpose [1]. As the number of high rise buildings is increasing, the international codes followed for building design, detailing and construction is revised quite frequently to adopt the new practices. Initiative has already been taken to update BNBC 1993 and a draft copy has already been prepared [2] called BNBC 2010 (draft). A total change at wind load and earthquake provisions in the proposed code can be noticed [1, 2]. This paper is aimed to review and compare the current and proposed seismic design provisions dealing with the specification of seismic design forces among the existing and recently proposed BNBC codes as well as other codes of different countries. The researcher have made a similar study [3] where they compared the BNBC 1993 code with contemporary codes like Uniform Building Code (UBC) 91 and UBC 97, National Building Code of India, 1983 (NBC India-83), and Outline Code of Bangladesh, 1979.

The method of calculation of seismic loading is more or less same in BNBC 2010 (draft) and BNBC 1993. Both these codes consider the earthquake force as a lateral force. The forces are determined on the basis of a base shear by Equivalent Lateral Force procedure. Base shear is calculated on the basis of seismic zone factor, structural importance factor and response reduction factor which is a function of structural system. Time period and soil type as a function of acceleration spectrum (Cs) defined by BNBC 2010 and as a function of numerical coefficient (C) defined by BNBC 1993 are used in the expression of base shear (Table 1). The base shear/weight ratios have been compared graphically with respect to the height of the building. NBC-India 2005 code also follows somewhat similar approach [3]. Base shear/weight ratios are computed from the given formula and hence plotted against height.

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In BNBC 1993, structure importance co-efficient is different for structural and non-structural components and equipment and denoted by I. But in BNBC 2010 (draft), importance co-efficient is denoted by I for all cases. In BNBC 1993, importance co-efficient is described for four different cases whereas it is described for five different cases in BNBC 2010. The descriptions of the cases in old and new codes are completely different. Importance co-efficient is found higher in BNBC 2010 and increased up to 25 % for some cases.

This is termed as site coefficient in BNBC 1993. The amount of ground motion amplification depends on wave-propagation characteristics of soils, which can be estimated from the measurements of shear wave velocity. Soft soils with slower shear wave velocities generally produce greater amplification than stiff soils with faster shear wave velocities. The site classes are defined mainly in terms of soil profile depth and shear wave velocity in the existing code. BNBC 2010 includes additional two procedures to determine the site classes as measuring shear wave velocity adds cost to a geotechnical investigation. Such classification is based on Standard Penetration Resistance, Untrained Shear Strength [8].

Code-based response spectrum is similar to Numerical coefficient of BNBC 1993 in a sense that both are functions of time period (T) and site characteristics (S). But2010 edition of the code introduces an additional parameter Damping Factor as a function of response spectrum. Damping factor is the effect of inherent energy dissipation mechanisms in a structure (due to sliding, friction, etc.) that results in reduction of effect of vibration, expressed as a percentage of the critical damping for the structure. BNBC 2010 suggests that 5 % damped design spectrum to be properly modified for an actual damping factor. BNBC 2010 introduces four equations each operating within a range of time period to determine Cs.

Seismic weight is the total dead load of building or structure, including partition walls, and applicable portions of other imposed loads. In BNBC 2010 (draft) a minimum of 25 % of live load is applicable for live load less than equal 3 KN/m2, otherwise 50 %. But in BNBC 1993 a minimum of 25 % of the floor live load shall be applicable irrespective of live load. Total weights of permanent equipments are considered in both codes. Allowance for partition wall is considered in BNBC 93 but it is not considered in BNBC 2010 (Draft). In Indian code seismic weight is the total dead load plus appropriate amounts of specified imposed load.

In Ultimate Strength Design method, the nominal earthquake loads are multiplied by a factor called Load Factor. They remain in combination with other loads and termed as Factored Load. The earthquake load combinations of the codes compared here are shown in the Table 4. After incorporating the corresponding maximum load factors of the BNBC 1993 and BNBC 2010, the previous graph is reconstructed and found like Fig. 2.

The vertical distribution of seismic forces of the BNBC 2010 is different from that of BNBC 1993. The BNBC 2010 prescribes a linear distribution and a parabolic distribution for structures with T 2.5 s respectively varying from a zero value at the base to a maximum value at the top. For intermediate periods, one may use a linear interpolation between a linear and a parabolic distribution, or a parabolic distribution which is more conservative. The BNBC 1993 code uses a linear distribution, with zero value at the base, for structures with T

Northern part of Bangladesh is surrounded by the regions of high seismicity which includes the Shillong plateau having possessed by multiple faults. Since these parts of Bangladesh and India can be characterized by the same tectonic features, computation of base shear for those zones following respective codes will highlight the design standards of these two countries against earthquake. Both BNBC (1993 and 2010) and NBC-India 2005 put the highest priority in these most severe earthquake prone zones by suggesting the highest seismic zone factor, Z = 0.36. Consideration of Soil with identical geotechnical features is important in comparing the base shear values as different types of soil subject to different sorts of ground motion. Soil type S3, SD and soft soil condition as per BNBC 1993, BNBC 2010 and NBC-India 2005 respectively is assumed for their identical geotechnical characteristics (N

Figure 3 is a plot of factored base shear for the maximum seismic loading that is governed by each of the respective codes and it shows proposed BNBC code exceeds the Indian code by some margins. Another graph (Fig. 4) is plotted below showing the seismic base shear for Jessore and Kolkata having similar tectonic and geological features but defined as low and moderate seismic intensity zone respectively in the respective codes. Due to the absence of Intermediate Moment Resisting Frame (IMRF) in the building system of the Indian code, Special Moment Resisting Frame (SMRF) as a lateral load resisting system is considered for moderate seismic risk. Soil type is assumed as before. Kolkata is found higher in terms of factored base shear.

According to the ASCE 7 05, each building is assigned to one of the six structural design categories (SDC) depending on risk category and the values of Ss and S1. On such basis, Sylhet is found to be under SDC D. The base shear/weight ratios are plotted for Sylhet following Equivalent Lateral Procedure which is applicable to a SDC D category building with no certain vertical or horizontal irregularities unless T > 3.5 Ts. Since BNBC 2010 and ASCE 7 05 have similar load factors, graph is plotted on the basis of nominal base shear. Existing BNBC 1993 code provides less base shear values compared to ASCE 7 05 standard. But the revised base shears in the proposed BNBC 2010 code will definitely be much closer to that of ASCE 7 05 standard (Fig. 5).

Therefore, this increase in factor of safety against the earthquake imposed by the proposed BNBC 2010 code by suggesting higher values of base shear is appreciable. But remarkably higher reinforcement requirement in ground floor column of low storied buildings than before might be a concern for building design in Bangladesh by the proposed code. Further studies need to be made in this aspect.

A building code is a set of rules that specify minimum standards for the construction of buildings. Buildings must conform to the code to obtain permission from the regulatory authority, usually from a local government body. The purpose of the code is to establish minimum standards for design, construction, quality of materials, use and occupancy, location and maintenance of buildings in order to safeguard, within achievable limits, life, limb, health, property and public welfare. The building code becomes law of a particular jurisdiction when formally enacted by the appropriate governmental authority.

Building codes are generally intended to be applied by architects, engineers, interior designers, constructors and regulators but are also used for various purposes by safety inspectors, environmental scientists, real estate developers, subcontractors, manufacturers of building products and materials, insurance companies, facility managers, tenants and others. Codes regulate the design and construction of structures where adopted into law. In Bangladesh, building codes are developed by the government agencies and then enforced across the country by the central government.

The first Bangladesh National Building Code was developed in 1993 and was enacted in 2006 followed by amendment of the Building Construction Act-1952. As a living document, the building code needs to be updated periodically within an interval of 4-5 years. The first developed and enacted BNBC has already been updated and is awaiting enactment as BNBC-2017. be457b7860