Top Structural Engineering Firm in Bangladesh
Structural Analysis and Design is the most important part of Building Design. The overall building stability depends on it. Cost Effective and safe design is the key responsibility of a structural Engineer. Proper analysis and design lead to a building’s safer Life and Low-cost construction. There are so many parameters to consider in Structural Analysis and Design. SHELLMARK LIMITED is the Top Structural Engineering Firm in Bangladesh. We are dealing with Structural Consultancy Services for more than 10 years in Bangladesh. We have designed more than 150 Structural designs all over Bangladesh. Bangladesh is situated in an active earthquake-vulnerable zone. So, earthquake-resistant building design is mandatory here. We consider earthquake and wind load while analyzing and design of building structures. There also have special detailing criteria for earthquake-resistant building design in BNBC-2020, Part-6, Chapter-8. We follow these detailing guidelines strictly in all of our structural detailing.
Our Structural Engineering Services:
- Residential Buildings
- Commercial Buildings
- Hospital and Medical College
- Residential Hotels and Resorts
- Educational Institutions
- Duplex and Triplex Villa House
- Vacation House and Firm House
- High Rise Building
- Pre-Engineered Steel Building
- Structural Retrofitting
- Earthquake Resistance Building
- Detailed Engineering Assessment (DEA)
- Mosque and Religious Building
- Sky Dining Restaurant
- Tall Skyscrapers
Our Structural Analysis and Design Process:
Step-01: Program Formulations:
In this step, We try to collect the general project information. Also, thoroughly review the Architectural Designs for the selection of Building Frame systems. We also, consider the Structural Irregularities n this Phase. Our project formulations are incredible to cover every step of our work in progress. The following considerations are noted down:
- Location of the Building
- Number of Stories
- Number of Basement Floors or not
- Number of Units on Each Floor
- Types of Occupancy/Building Use
- Types of Foundation Soil
- Height of Plinth Level
- Types of Exposures
- Surrounding Structures
- Floor-to-Floor Height
- Roof Top Usage
- Use of Ground Floor
Step-2: Selection of Framing Systems:
In this step, we try to select the Building heights and framing systems as per Architectural. There are different types of building Framing systems are listed below:
- Load Bearing System
- Beam, Column System
- Beam, Column & Shear Wall System
- Tubular Structural System
- Branched Tube System
- Tube in Tube System
- Bundle Tube System
Step-3: Selection of Foundation Type:
After analyzing and reviewing the soil Test report, we select a preliminary Foundation Type. The Foundation type depends on the bearing capacity of the subsoil. There are two types of Foundations:
- Shallow Foundation-Footing Foundation
- Deep Foundation-Pile Foundation
Step-4: Load Calculation of Building:
Load calculation is the most important part of Structural Design. An experienced Structural Engineer always calculates the superimposed load in an efficient way. We are the Top Structural Engineering Firm in Bangladesh with more than 10 years of experience. Different types of loads are calculated in Building Design are listed below:
- Dead Loads-Self Weight of Building, Fixed Walls, Fixed Furniture, Fixed Equipment, etc.
- Live Loads – Human Loads, Temporary Partitions, Moveable Furniture, Moveable Equipment Floor Finish, False Ceiling, etc.
- Earthquake Load – Load Due to Earthquake
- Wind Load- Load Due to Wind Flow or Surge
- Snow Load- Load Due to Snow Fall
- Rain Load- Load Due to Rainfall
- Temperature Load- Load Induced Due to Change in Temperature
Step-5: Structural Analysis:
In this step, we perform the structural analysis to compute the Moment, Shear, and Torsion for each member. We also compute the support reaction from the analysis result, which is used for foundation design. Also, calculate the top defection of the building and story drift to the allowable limit.
Step-6: Structural Design:
We use the Structural Analysis output data for Structural Design. We design the Individual members Like Beams, Columns, Slabs, and Shear Walls according to the Shear, Moment, and Tensional Forces. Finally, we design to find the size of members and quantity of reinforcement. We also, consider the concrete strength and yield strength of reinforcement in structural design. Safe and economic design is the key target of an experienced Structural Engineer.
Step-7: Drafting and Printing:
At last, we interpret the designed data with Auto CAD Drafting Software. Try to compute the step-by-step design data in separate sheets with proper detailing and specifications. Finally, we deliver the design sheets to the client in printed formats.
Structural Analysis and Design is a methodological work with sophisticated calculations. A small error caused a huge risk. An experienced structural Engineering company may handle the whole process carefully. SHELLMARK LIMITED is the Top Structural Engineering Firm in Bangladesh. We are working as a Structural Engineering service provider company for more than a decade. Our experience Structural Engineers are capable of handling the design process of any type of building structure.
Types of Load Considered in Structural Design in Bangladesh.
There are different types of load described in the Bangladesh National Building Code(BNBC-2020). Most Structural Engineers invest lots of time to find out the specific load acting on structures. Efficient Structural Analysis and Design depend on appropriate calculations of load types and consecutive intensity. The behavior and application of load on structures are also important issues. There are different types of load according to their applications. Uniformly Distributed Loads, Line Loads, and Concentrated Loads are most of them. We have conducted more than 150 structural designs in the last 10 years. Today SHELLMARK is the Top Structural Engineering Firm in Bangladesh.
1. Dead Loads
A Dead Load of a building is the vertical load. Generally, Dead Loads are fixed in their positions. Self-weight of all structural and non-structural members is considered a dead load. The weight of permanent partition walls and fixed service equipment are also treated as dead load. In the case of pre-stressing members, the net effect of pre-stressing is taken as the dead load. The efficient calculation of Dead Load will allow a cost-effective design for your building.
2. Live Loads
Live Loads of a building are considered both vertical and horizontal loads. Generally, live loads are moveable and superimposed on the building structures. Live loads come from the occupancy of the building. The temporary partition walls and moveable service equipment are treated as live loads. Live loads must be different according to the occupancy of the building. As per BNBC-2020, Live Loads for a residential Flat in 2 KN/m2. For the office building, the live load is 2.4 KN/m2. Live loads may be uniformity distributed, line loads, or point loads.
3. Wind Loads
Wind loads of the building are basically lateral loads. These loads induced by the horizontal wind flow act on the building surface. The wind loads are calculated on the basis of basic wind speed. Basic wind speeds are variable in different locations in Bangladesh. As per BNBC-2020, basic wind speed for Dhaka is 65.7 m/s, Chittagong 80 m/s, Khulna 73.3 m/s, and so on. The wind pressure of a building depends on the exposure category.
4. Earthquake Loads
Earthquake loads of a building are induced due to seismic activity. This type of load act on the base of a building horizontally. Earthquake Resistant buildings are designed in accordance with peak ground acceleration. The whole of Bangladesh is divided into four Zones according to seismic intensity. They are classified as Zone-01: Low Vulnerable, Zone-02: Moderate Vulnerable, Zone-03: Severe Vulnerable, and Zone:-04: Very Severe Vulnerable. The seismic zone co-efficient is also different for that zone. The zone co-efficient Z=0.12, Z=0.20, Z=0.28, Z=0.36 for Zone-01 to Zone-04 respectively.
5. Miscellaneous Loads
There are also some secondary loads that act on building structures. Rain Loads, Fluid Loads, Snow Loads, and Loads due to temperature effects are considered miscellaneous loads. These loads have fewer impacts on building in Bangladesh. Bangladesh does not experience snowfall in the winter season. So the effect of snowfall can be overlooked during structural analysis and design.
Earthquake Resistant Structural Design Provision in Bangladesh.
The primary purpose of Earthquake Resistant Building Design is to provide sufficient lateral stiffness for Building Structures due to earthquake forces. Bangladesh National Building Code(BNBC-2020) has proper and specific guidelines for analyzing and designing Building Structures due to Earthquake Loads. The whole of Bangladesh is divided into four seismic zones according to seismic vulnerability. Each zone has a different zone coefficient. The zone coefficient provides expected peak Ground Acceleration corresponding to Maximum Considered Earthquake (MCE). SHELLMARK is the Top Structural Engineering Firm in Bangladesh to conduct earthquake-resistant building designs according to the latest codes.
Earthquake Resistant Structural Design Provision in Bangladesh.
1. Seismic Zone Co-efficient:
According to seismic intensity whole of Bangladesh is divided into 4 seismic zones. Each zone has a separate zone co-efficient. The different zones and zone coefficients are described below:
The southern part of Bangladesh is considered the Zone-01 in seismic zoning Map stated in BNBC-2020. Barisal, Khulna, Jashore, and Rajshahi are major areas under Zone-01. This zone is considered the low Earthquake Vulnerable Zone. The zone co-efficient is Z=0.12
The lower Central and Northwestern parts of Bangladesh including Noakhali, Dhaka, Pabna, and Dinajpur are considered under this zone. Also, the southwestern part of Bangladesh including the Sundarbans lies under this zone. This zone is considered a moderate vulnerable zone. The zone co-efficient is Z= 0.20
The upper central and northwestern parts of Bangladesh including Brahmanbaria, Sirajgonj, and Rangpur are Considered under Zone-03. This zone is treated as a severely vulnerable zone. The zone co-efficient in Z= 0.28. Extra care must be taken while designing buildings under this zone.
The Northeastern part of Bangladesh including Sylhet, Mymensingh, and Kurigram lies in Zone-4. This zone is in a very severely vulnerable zone. The zone co-efficient Z= 0.36. Special seismic detailing can be assured for building structures under this zone.
Town wise seismic zone co-efficient are listed in below Table:
2. Local Soil Condition:
Earthquake load is directly imposed on the base of the Building Structures. There are 7 types of site classifications based on soil properties up to 30 m depth. The site classifications are directly related to the average shear wave velocity of soil, the SPT- N values, and the undrained shear strength of the soil. The site classifications based on soil properties are described below:
This type of site contains Rock or rock-like soil including 5m of weaker soil at the top surface. The shear wave velocity is more than 800 m/s under this site favorable for the construction of Earthquake Resistant Buildings.
This type of site comprises deposits of very dense sand, gravel, or very stiff clay. This site is characterized by a gradual increase of Mechanical properties of soil with depth. The shear wave velocity of soil under this site is 360 m/s to 800 m/s. The SPT-N values are greater than 50 and the undrained shear strength is more than 250 Kpa.
Site Class- SC:
This site class contains deep deposits of dense or medium-dense sand, gravel, or stiff clay with thicknesses from several tens to many hundreds of meters in depth. The shear wave velocity is 180 m/s to 360 m/s. The SPT-N values are 15 to 50 and undrained shear strength is 70 Kpa to 250 Kpa.
Site Class- SD:
This type of site contains deposits of loose to medium cohesion less soil or predominantly soft to firm cohesive soil. The shear wave velocity is less than 180 m/s. The SPT-N values are less than 15 and the undrained shear strength of the soil is below 70 Kpa. This type of site condition is very disfavored to Earthquake Resistant Building Design.
Site Class- SE:
This site class contains a soil profile consisting of a surface alluvium Layer with shear wave velocity of type SC or SD class. The thickness of the soil very Between 5m to 20m, underlain by more than 800 m/s.
Site Class- S1:
This type of site contains deposits containing a layer of at least 10m thick soft clay/silt with a high Plasticity Index value and high-water content. The Plasticity Index is more than 40.
Site Class- S2:
This type of site contains the deposits of liquefiable soils, sensitive clays, or any other soil profile not included in site class SA to S1
3. Response Modification Factor(R):
The Effect of Earthquake Loads on structures related to the Response Modification Factors. It is denoted by “R”. The response modification factor values are different according to the moment-resisting capacity of Building frames. There are 3 types of moment-resisting frames. Firstly, special Moment Resisting Frame (SMRE). Secondly, intermediate moment resisting Frame (IMRF). Thirdly, Ordinary Moment Resisting Frame (ONRF). The different moment Resisting Frames and Response Modification Factors are described below:
Special Moment Resisting Frame(SMRF):
Any building structures assigned to the seismic design category SDC D are to be designed as SMRF. This type of structure should have some special seismic detailing stated in BNBC-2020, Part-VI, Chapter -8. The value of response modification factor R=8. Slabs without beams are not permitted in the SMRF system. The interactions between structural and non-structural members are to be considered in structural analysis.
Intermediate Moment Resisting Frame(IMRF):
Any building structures to be built on seismic design category SDC C must comply with the design criteria of IMRF. The Response modification factor R=5. For IMRF. Intermediate structural Detailing criteria are to be maintained for all structural members. Under this type of framing system, buildings are expected to resist inelastic deformations in its member and joints.
Ordinary Moment Resisting Frame(OMRF):
This type of framing system can be built on low-vulnerable seismic intensity areas. OMRFs are considered to undergo little or negligible inelastic deformation under earthquake loads. The value of response modification factor R= 3 for OMRF. No special seismic detailing is required for OMRF. But care must be taken while designing beam Column connections.
4. Importance Factors of Building:
In Earthquake Resistant Building Design, Buildings are classified into four categories according to the structural importance factor. The structural importance factors depend on the consequences of collapse for human life, and the importance of public safety and protection measures during the post-earthquake period. It also depends on the social and economic impact very soon after an earthquake disaster. Depending on the occupancy category, a building must be designed for higher seismic forces using the importance factor. The structural importance factor is denoted by “I”. The values of I are different for various occupancy categories. I = 1.0 for company categories I & II. I = 1.25 for category III and I = 1.50 for occupancy category IV. SHELLMARK LIMITED is the Top Structural Engineering Firm in Bangladesh.
5. Building Irregularity:
Building Irregularity severely affects earthquake forces. Buildings with irregular plans and elevations are more vulnerable than buildings with regular configurations. There are two types of building irregularity –
A. Plan Irregularity:
There are different types of plan irregularity in building structures are listed below-
- Torsion Irregularity
- Re-entrant Corner
- Diaphragm Discontinuity
- Out-of-plane offsets
- Non-parallel systems
B. Vertical Irregularity:
Building may be irregular in vertical elevations. This type of irregular shape affects the earthquake response of a building. The vertical irregularity are listed below-
- Stiffness Irregularity – Soft Story
- Mass Irregularity
- Vertical Geometrical Irregularity Discontinuity
- Vertical In-plane Discontinuity
- Capacity Discontinuity-Weak Story
6. Types of Structural Systems:
The selection of structural systems in earthquake-resistant building design is an intellectual task. There are some deflection Limits and height limitations for each structural system. There are 7 structural systems considered in Earthquake Resistant Building Design listed below-
A. Bearing wall systems (No-Frame)
B. Building Frame Systems (With bracing or shear wall)
C. Moment Resisting Frame Systems (No shear wall)
D. Dual Systems-where Special Moment Frames are capable of resisting at least 25% of prescribed seismic forces. (With bracing or shear wall)
E. Dual systems – where Intermediate Moment Frames are capable of resisting 25% of prescribed seismic forces (with bracing or shear wall)
F. DualShear Wall Frames Systems
G. Steel Systems not specifically detailed for seismic resistance