International Journal of Science, Engineering and Technology Research (IJSETR)
Volume 1, Issue 1, July 2012
[(]
Comparative Study on Failure Members of Multi-Storey RC Building under Wind Loads
Thae Nu Aye, Dr. Zaw Min Htun
Abstract— This study mentions the comparative study on analysis and design of wind effected multi-storeyed reinforced concrete building. All structural members are designed with ultimate strength design based on ACI 318-99 code. The proposed building is irregular U shaped twelve storeyed building which is situated in seismic zone 2A and its height is 129ft above ground level. The proposed building is intermediate moment resisting frame. The structure is analyzed under dead loads, live loads, wind loads and earthquake loads by using UBC 97. This study is done to know storey responses related to five wind speeds of 80 mph, 95 mph, 110 mph, 130 mph and 155 mph according to cyclone categories. The stability of the structure such as storey drift, overturning moment, sliding, torsional irregularity and P-∆ effect is satisfied for basic wind speed 80 mph. As a result, the percentage of failed members and story responses related to five different wind speeds are summarized in this study.
Index Terms— ACI 318-99, Various Wind Load, Failure Percent, ETABS Software
I. Introduction
Nowadays global warming is generating climate changes. Some areas of the world are experiencing natural disasters. These are storms, floods, draught, heat waves, earthquakes, and tsunamis due to seasonal changes. Myanmar has witnessed some of the deadliest storms in the Bay of Bengal. The country is hit by a storm every 1 or 2 years. Similarly, Nargis which is a natural disaster that hit Myanmar in 2008 caused very high casualty of human lives, animals and properties. Nowadays, many areas in Myanmar are subjected to frequent environmental effects especially wind load and earthquake load. Therefore, the design for structures in Myanmar must be safe, serviceable and resistant to forces caused by wind effects and seismic effects. In this study, wind loads are emphasized other loads. In addition, the high coast of land, the desire to avoid a continuous urban sprawl and the need to preserve important agricultural production have all contributed to construct various type of multi-storeyed buildings. According to the requirement of country, we should design and construct high-rise buildings which are more technically. Coastal and delta regions of Myanmar are prone to seasonal storms. Moreover, residential building can suffer extensive wind damage which they are improperly designed and constructed and when wind speeds exceed design levels. So, designer engineer should be considered about the effects of wind load on building. All Structures are designed and constructed to resist collapse and permanent lateral movement due to action of loads from wind load. In this proposed building, location is earthquake zone 2A and basic wind speed with 80mph is basically designed. In this study, the analysis results of the reinforced concrete building under different wind speeds are investigated.
II. Objective of the Study
1. To realize the influence of wind speed for irregular reinforced concrete building in seismic zone 2A
2. To analyze and design of wind effected U shaped twelve- storeyed reinforced concrete building
3. To compare the analyzed result and failed member of proposed building due to various wind speed
III. Wind Effects on Building
Windy weather poses a variety of proplems in new skyscrapers, causing concern for building owners and engineers alike. The forces exerted by winds on buildings increase dramatically with the increase in building heights. Static wind effects increase as the square of astructure’s height. Moreover, the velocity of wind increases with height, and the wind pressures increase as the square of the velocity of wind. Thus, the wind effects on a tall building are compounded as its height increases.
In designing for wind, a building cannot be considered independent of its surrounding. The influence of nearby buildings and of the land configuration can be substantial. Most wind damage to building occur in high wind High winds are capable of imposing large lateral (horizontal) and uplift (vertical) forces on buildings. Residential buildings can suffer extensive wind damage when they are improperly designed and constructed and when wind speeds exceed design levels. The effects of high winds on a building will depend on several factors:
(1) Geographical location proximity of other obstructions to air flow
(2) Exposure or shielding of building relative to wind direction
(3) Wind speed and duration of high wind
(4) Height of building above ground
(5) Strength of the structural frame, connections and envelope
(6) Shape of building and building components
(7) Number, size, location and strength of openings
(8) Type, quality and velocity of windborne debris.
The wind speed due to topographic effects can occur wherever mountainous, areas, gorges, and ocean promontories exit. The wind speed increase near the crests of high coastal bluffs, cliffs or dunes or in gorges and canyons.
IV. Preparation for the Proposed Building
A. Site Location and Structural System
Location : Seismic zone 2A
Type of Structure : Twelve Storeyed Reinforced Concrete Building
Type of Occupancy : Residential
Plan Dimension : X direction = 120ft
: Y direction = 94ft
Height of Structure : 129ft
Typical story height : 10 ft
Bottom story height : 12 ft
Shape of Structure : U shaped
Number of Elevator : 2 numbers
Fig.1 Typical floor plan for proposed building
Fig.2 3D view for proposed building
B. Material Properties
Analysis property data
Weight per unit volume of concrete : 150pcf
Modulus of elasticity : 3.122x106psi
Poisson’s ratio : 0.2
Coefficient of thermal expansion : 5.5x106in/in per
degree F
Design property data
Reinforcing yield stress, fy : 50000psi
Shear Reinforcement yield stress,fy : 50000psi
Concrete cylinder strength, fc′ : 3000psi
C. Loading consideration
The structure is defined gravity loads and lateral loads. The gravity loads consist of dead load, live load. The lateral loads contain wind load and earthquake load. Self-weights of all elements put in are considered as dead loads. Floor finishing, ceiling, partitions are considered as superimposed dead loads. Earthquake loads and wind loads are designed according to UBC97.
1) Dead Loads
Data for dead loads are as follows:
- Unit weight of concrete = 150 psf
- 4.5inches thick brick wall weight = 55 psf
- 9 inches thick brick wall weight = 100 psf
- Weight of elevator = 2 tons
- Weight of slab = 25 psf
2) Live Loads
Data for live loads are as follows:
- Live load on residential areas = 40 psf
- Live load on landing = 100psf
- Live load on public areas = 100 psf
- Live load on roof = 20 psf
-Weight of water = 62.4 pcf
3) Wind Loads
Data in designing for wind load:
- Exposure type = Type D
- Basic wind velocity = 80 mph
- Height = 129ft
- Method used = Normal force method
- Importance factor = 1.0
- Windward coefficient = 0.8
- Leeward coefficient = 0.5
4) Seismic Loads
Required data for earthquake load:
-Seismic zone = 2A
- Seismic zone factor = 0.15g
- Soil profile Type = SD
- Seismic Response Coefficient, Ca = 0.22 Na
- Seismic Response Coefficient, Cv= 0.32Nv
- Near Source factor, Na = 1
- Near Source factor, Nv = 1
- Framing system = IMRF
- Response modification factor, R = 5.5
- Numerical coefficient, Ct = 0.03
-Analysis Type = Static analysis
V. Design Result of Proposed Building with Static Analysis
The beam, column section and layout plan of the proposed building with design basic wind speed 80 mph are list in Table I, II and appendix.
Table I
Design Sections of Beam
Beam Name / Storey Level / Beam Size(in x in )
B1 / All story / 10 x 12
B2 / All story / 10 x 14
B3 / All story / 10 x 18
B4 / Ground Floor to Twelfth Floor / 12 x 16
Roof / 10 x 12
B5 / All story / 12 x 18
B6 / Ground Floor to Eighth Floor / 14 x 16
Ninth Floor to Twelfth Floor / 12 x 16
B7 / Ground Floor to Seventh Floor / 14 x 18
Eighth Floor to Twelfth Floor / 12 x 18
SB1 / All story / 10 x 12
SB2 / All story / 10 x 14
SB3 / All story / 12 x 14
SB4 / All story / 12 x 18
Table II
Design Sections of Columns
Column Name / Storey Level / Column Size(in x in)
C1 / GF to 2F / 18 x 18
3F to 4F / 16 x 16
5F to 6F / 14 x 14
7F to 12F / 12 x 12
C2 / GF to 3F / 22 x 22
4F to 9F / 18 x 18
10F to 12F / 12 x 12
C3 / GF to 3F / 18 x 18
4F to 6F / 16 x 16
7F to 9F / 14 x 14
10F to 12F / 12 x 12
C4 / GF to 3F / 14 x 14
4F to 12F / 12 x 12
C5 / GF to 3F / 20 x 20
4F to 6F / 18 x 18
7F to 9F / 16 x 16
10F to 12F / 12 x 12
C6 / GF to 3F / 18 x 18
4F to 6F / 16 x 16
7F to 9F / 14 x 14
10F to ROOF / 12 x 12
C7 / GF to 1F / 24 x 24
2F to 3F / 22 x 22
4F to 6F / 20 x 20
7F to 9F / 18 x 18
10F to 12F / 14 x 14
ROOF / 12 x 12
C8 / GF to 3F / 20 x 20
4F to 6F / 18 x 18
7F to 9F / 16 x 16
10F to 12F / 12 x 12
C9 / GF to 3F / 18 x 18
4F to 6F / 16 x 16
7F to 12F / 12 x 12
C10 / GF to 3F / 22 x 22
4F to 6F / 20 x 20
7F to 9F / 16 x 16
10F to 12F / 12 x 12
C11 / GF to 3F / 24 x 24
4F to 6F / 20 x 20
7F to 9F / 16 x 16
10F to 12F / 12 x 12
VI. Checking for Stability of the Structure with Design Wind Speed 80 Mph
After applying loading, the structure is deformed due to loading and the Structure is needed to check the following for the stability of the proposed building. The UBC-97 states that the P-delta effect needs not to be considered when the ratio of storey drift to storey height does not exceed 0.02/R in seismic zone 3 and 4. In checking for sliding, when the ratio of resistance due to friction to sliding force, V is greater than or equal to 1.5, the design is safety. Checking for P-delta effect and sliding are within the design limit. In checking for overturning, the ratio of resisting to overturning moment of the building is greater than 1.5. So, the overturning moment checking is safety. In checking for storey drift, it is found that storey for all storey do not exceed limit. In proposed building, the maximum drift at one end of the structure transverse to its axis is not more than 1.2 times the average storey drifts of both ends. Therefore the effect of torsional irregularity can be neglected. Therefore, the proposed building is satisfied for all stability check.
VII. RESULTS OF FAILED MEMBERS with Various Wind Speed
In this study, the proposed building is initially designed with basic wind speed of 80 mph. And then, this model is also designed with four different wind speeds (95 mph, 110 mph, 130 mph and 155 mph) in order to know wind effect on the building and failed members in each design wind speed without changing frame member sizes. When the design wind speed of building is increased, the building is not satisfied with structural stability criteria. The whole structure consists of 1479 beams and 722 columns. When other different wind speeds are considered, 190 numbers of beams and 2 numbers of columns are failed in 95 mph and 510 beams and 42 columns are failed in 110 mph. 776 beams and 151columns are failed in 130 mph and 953 beams and 326 columns in 155 mph. So, numbers of failed members in 120 mph and 150 mph are summarized in Table III and IV. Moreover, percentages of failed members are graphically represented in Figure 3.
Table III
Number of Failed Beams in Each Storey
Storey / Number of Failed BeamWind Speed
80 mph / 95 mph / 110 mph / 130 mph / 155 mph
1 / - / 19 / 65 / 102 / 108
2 / - / 41 / 94 / 106 / 112
3 / - / 40 / 94 / 105 / 112
4 / - / 41 / 92 / 100 / 108
5 / - / 27 / 61 / 100 / 108
6 / - / 14 / 47 / 96 / 104
7 / - / 8 / 33 / 74 / 100
8 / - / - / 15 / 50 / 91
9 / - / - / 6 / 25 / 65
10 / - / - / 2 / 12 / 33
11 / - / - / 1 / 4 / 10
12 / - / - / - / 2 / 2
Roof / - / - / - / - / -
Total Failed no / - / 190 / 510 / 776 / 953
Table IV
Number of Failed Columns in Each Storey
Storey / Number of Failed ColumnWind Speed
80 mph / 95 mph / 110 mph / 130 mph / 155 mph
1 / - / 2 / 22 / 50 / 59
2 / - / - / 6 / 18 / 37
3 / - / - / 2 / 10 / 21
4 / - / - / 4 / 19 / 37
5 / - / - / 4 / 14 / 35
6 / - / - / - / 4 / 19
7 / - / - / 4 / 24 / 48
8 / - / - / - / 10 / 33
9 / - / - / - / - / 10
10 / - / - / - / 2 / 27
11 / - / - / - / - / -
12 / - / - / - / - / -
Roof / - / - / - / - / -
Total Failed no / - / 2 / 42 / 151 / 326
Fig.3 Percentage of Failed Members (Beams and Columns)
From the analysis data, the highest number of failed beams and columns is occurred in the highest wind speed 155 mph. The failures of the whole building due to various wind speed are described graphically by percentage as shown in figure 4.