Building Assessment Criteria
INTRODUCTION:
The Building Assessment is a RCC frame structured building with roof shed. The owner has supplied the structural drawings with which the building is constructed. The submitted drawings were thoroughly examined in order to identify the structural and foundation system of the building. Site interview is also taken. A set of as-built architectural drawings has been prepared by means of necessary survey work with in situ measurements. The structural analysis of the building was performed using finite element software Etabs & Staad.Pro v8i for DEA with the as built architectural and structural drawings with which the building has been functioning as single storied factory building.
SCOPE OF WORK:
As asked by the client, the scope of work is to verify the safety of columns of the existing Steel shed Building. Maximum load combinations likely to be experienced by the building during its lifetime are included in detailed structural analysis. Checking of different column members was conducted on the basis of actual strength of steel used in construction.
The scopes of the work are as follows:
1. Physical survey for observing visible condition of the building, finding defects or cracks, if any in structural and non-structural member & any foundation settlement.
2. Detailed survey of the Building Assessment for preparing as built architectural drawings and for verifying all measurement indicated in the as built structural drawings supplied with us.
3. Finite element modeling of the building and detail analysis of the building using Staad Pro. Computer program.
4. Checking the structural capacity of columns using analysis results obtained from analysis model.
METHODOLOGY
The assessment of the existing structures can be carried out with methods of varying sophistication and effort. The core objectives, as described above, are to analyze the current load carrying capacity and to predict the future performance with a maximum of accuracy and a minimum of effort.
In most cases it judiciously to start with simple conservative routines and use more sophisticated routines only when the evaluated load carrying capacity is insufficient. Generally structural assessment should be carried out using limit state principles with characteristic values and partial safety factors. If more refined methods are necessary, the probabilistic approach has to be applied, if economic.
If structures have failed assessment to an acceptable capacity, the engineer can make a recommendation, but the technical authority is likely to be ultimately responsible for public safety and therefore has to do the final decision. A structure, failed in assessment, may remain in service if it presents a low risk, subject to monitoring.
FIELD OBSERVATIONS
To reduce uncertainties about load and resistance, site specific data should be used within the analysis process. Very effective methods are site inspection.
Under inspection building geometry, member shape & size, connections, load and resistance parameters and overall building condition is observed. Following things are noted while site assessment is done –
1. Building dimension & grid dimension are collect by field survey. In analysis average dimension are taken. Those are also presented in as built drawing.
2. Engineers from MAK CONSULTANTS visited the building and have examined all beams, columns, Rafter, Purlin and Roof arrangement. They have also measured spacing of columns, dimensions of beams, columns, Rafter, purlin and other structural elements. Plan area of the buildings as surveyed was found to be very much close to the Arch drawing of the buildings.
3. MAK CONSULTANTS Engineers checked a number of columns of the building. Columns, which are the main vertical and load bearing component of a building has no sign distress or cracking anywhere in the building.
Inspections and material testing
To reduce uncertainties about load and resistance, site specific data should be used within the analysis process. Very effective methods are site inspection and material testing.
Under inspection building geometry, member shape & size, connections, load and resistance parameters and overall building condition is observed.
Though the main objective was to perform analysis & prepare design calculation on the constructed structure, present conditions of structural members are also considered. During visual Inspections some deterioration processes like corrosion are observed.
Material tests are done for determining strength parameter of the used building material. The tests can be destructive and non destructive. They can be conducted on site or at a laboratory.
Under this process no materials test is done for reinforcing steel for difficulties in sample collection & several type of tests are done for Concrete.
Applicable Codes & References:
The building is designed in accordance with the following codes of Accord alliance that dictate the design of buildings.
Loads on all buildings are applied in accordance with:
Bangladesh National Building Code (BNBC-2006)
Guidelines for Assessment of Structural Integrity of Existing RMG Factory Building in Bangladesh
Technical Committee of National Tripartite Working Group,
National Tripartite Plan of Action on Fire Safety & Structural Integrity Building Code Requirements for Structural Concrete (ACI 318-13)
American Concrete Institute,
38800 Country club Drive Farmington Hills, MI -48331.Strength Evaluation of Existing Concrete Buildings (ACI 437R-03)
American Concrete Institute,
38800 Country club Drive Farmington Hills, MI -48331.
Guide for Obtaining Cores and Interpreting Compressive Strength Results (ACI 214.4R-03)
American Concrete Institute,
38800 Country club Drive Farmington Hills, MI -48331.
In-Place Methods to Estimate Concrete Strength (ACI 228.1R-03)
American Concrete Institute,
38800 Country club Drive Farmington Hills, MI -48331.
Assumptions /Considerations:
Support system is considered pin.
Floor slab is considered as semi-rigid Diaphragm.
All structural members are rigidly connected at joints for RCC elements.
In-fill brick wall has no contribution on rigidity of the structure.
Continuous lintels are not considered as structural element.
Stair is considered as one way plate element.
Only centre line dimensions are taken.
The following two loading conditions are considered a) Gravity load b) gravity along with lateral load.
Special Consideration
After analysis with specified strength reduction factors (Ø) & load factors (ψ), it is observed that the structure is not compatible. Most of the members compatible except few columns are over stressed. For that we have to go for further analysis using revised strength reduction factor. For that section 20.2.5 of ACI318-08 is used. Under this evaluation When If the required dimensions and material properties are determined through measurements and testing, and calculations are be made in accordance with 20.1.2, it shall be permitted to increase φ from those specified in 9.3, but φ shall not be more than:
Tension-controlled sections,
As defined in 10.3.4 ..............................................1.0
Compression-controlled sections,
As defined in 10.3.3:
Members with spiral reinforcement
Conforming to 10.9.3 ..........................................0.9
Other reinforced members .................................0.8
Shear and/or torsion .............................................0.8
Bearing on concrete .............................................0.8
General
To reduce uncertainties about load and resistance, site specific data should be used within the analysis process. Very effective methods are site inspection and material testing.
Material tests are done for determining strength parameter of the used building material. The tests can be destructive and non destructive. They can be conducted on site or at a laboratory.
Under this process materials test is done for concrete. For difficulties in sample collection for steel no tests are done for reinforcing rebar.
Material Test:
Reinforcing Steel
Since, it was not possible to gather test sample of reinforcing bar, tension test was not possible. For that, it was considered that yield strength of rebar is 40ksi.
Concrete
For determining concrete strength ACI 562 method is followed.
Since, after performing these tests, combining results from more than one in-place test, a multivariable correlation is established to estimate strength. Combined methods are reported to increase the reliability of the estimated strength. Details Literature, results & interpretations are provided in appendix-i.
After finding concrete strength from several spots, finally the core strength is determined as per ACI 562 according to equation 6.4.3.
Where, fc = is the average core strength modified to account for the diameter and moisture condition of the core;
V = is the coefficient of variation of the core strengths;
n= the number of cores taken;
Kc = the coefficient of variation modification factor,
EXCAVATION OF FOUNDATION
From previous foundation drawings, it is seen that existing foundation of the building is isolated column footing (shallow foundation). To evaluate the size, depth and other parameters, footing of two columns footing are excavated. After excavating it is found, the footings size is rectangular.
Pictorial Evidence
The photographic materials not only constitute a unique evidence /documentation of the investigation or verification project, but also the important instrument for graphical computation. In many ways the photographs were determinative. The objective of the present project is to verify foundation of concern building, especially verification of as-built drawing. For this purpose time-line photographs are taken. Selected photos are presented in this report.
Modeling & Analysis
Depending on the type of project, there are several well-established methods among which Finite Element Method (FEM) is perhaps the most sophisticated and all-encompassing one. For analysis and design checking of the building, powerful finite element based structural design software package ETABS-V9.7 has been employed for analysis. A full three dimensional modeling of the structure has been developed using frame and plate/shell elements.
Modeling:
A number of analyses were used to assess the response of the foundation for the Structure. The main design model was developed using a Finite Element (FE) program Etabs 9.7.3. A summary of the model set up is as follows:
Soil Support: Soil is considered as continuum medium. While modeling, support is considered as fixed.
Shearing Action: Applied as a body load to the structure foundation elements, in a direction to coincide with the appropriate wind action assumed;
Building Stiffness Effect: Superstructure shear walls (not interrupted at door openings) were modeled as a plate elements overlaid on the tower shallow foundation elements. The moment of inertia was modified to simulate the stiffening effect of the structure.
Slab Element: Floor slabs are considered semi-rigid diaphragm and modeled as shell elements. Stiffness is modified. Membrane stiffness is used full scale, while bending stiffness is almost ignored.
Design Input:
Analysis process of the structure was carried out with following input:
Material Properties
Table 4-1 : Material Properties in simulation
M A T E R I A L P R O P E R T Y D A T A
MATERIAL MATERIAL DESIGN MATERIAL MODULUS OF POISSON'S THERMAL SHEAR
NAME TYPE TYPE DIR/PLANE ELASTICITY RATIO COEFF MODULUS
STEEL Iso Steel All 29000.000 0.3000 6.5000E-06 11153.846
CONS1 Iso Concrete All 3149.000 0.2000 5.5000E-06 1312.083
OTHER Iso None All 29000.000 0.3000 6.5000E-06 11153.846
CONC1 Iso Concrete All 3402.000 0.2000 5.5000E-06 1417.500
CONB1 Iso Concrete All 3815.000 0.2000 5.5000E-06 1589.583
M A T E R I A L P R O P E R T Y M A S S A N D W E I G H T
MATERIAL MASS PER WEIGHT PER
NAME UNIT VOL UNIT VOL
STEEL 7.3240E-07 2.8300E-04
CONS1 2.2460E-07 8.6800E-05
OTHER 7.3240E-07 2.8300E-04
CONC1 2.2460E-07 7.8130E-05
CONB1 2.2460E-07 7.8130E-05
M A T E R I A L D E S I G N D A T A F O R S T E E L M A T E R I A L S
MATERIAL STEEL STEEL STEEL
NAME FY FU COST ($)
STEEL 50.000 65.000 1.00
M A T E R I A L D E S I G N D A T A F O R C O N C R E T E M A T E R I A L S
MATERIAL LIGHTWEIGHT CONCRETE REBAR REBAR LIGHTWT
NAME CONCRETE FC FY FYS REDUC FACT
CONS1 No 3.000 40.000 40.000 N/A
CONC1 No 2.267 40.000 40.000 N/A
CONB1 No 2.024 40.000 40.000 N/A
ETABS v9.7.3 File:01 BCL RCC_DEA ALIANCE 42 Units:Kip-in October 27, 2015 13:39 PAGE 2
Section Properties
Table 4-2 : Section Properties
F R A M E S E C T I O N P R O P E R T Y D A T A
F R A M E S E C T I O N P R O P E R T Y D A T A
MATERIAL SECTION SHAPE NAME OR NAME CONC CONC
FRAME SECTION NAME NAME IN SECTION DATABASE FILE COL BEAM
C1BG-14X14 CONC1 Rectangular Yes
FB1-10X24 CONB1 Rectangular Yes
C2BG-12X12 CONC1 Rectangular Yes
GB-12X20 CONB1 Rectangular Yes
C1AG-12X12 CONC1 Rectangular Yes
C2AG-10X10 CONC1 Rectangular Yes
FB1234-12X15 CONB1 Rectangular Yes
FB2-10X18 CONB1 Rectangular Yes
FB5-12X23 CONB1 Rectangular Yes
C3AG-21X13 CONC1 Rectangular Yes
C3BG-23X15 CONC1 Rectangular Yes
C4BG-14X14 CONC1 Rectangular Yes
C4AG-12X12 CONC1 Rectangular Yes
C5BG-22X14 CONC1 Rectangular Yes
C5AG-20X12 CONC1 Rectangular Yes
F R A M E S E C T I O N P R O P E R T Y D A T A
SECTION FLANGE FLANGE WEB FLANGE FLANGE
FRAME SECTION NAME DEPTH WIDTH TOP THICK TOP THICK WIDTH BOT THICK BOT
C1BG-14X14 14.0000 14.0000 0.0000 0.0000 15.0000 0.0000
FB1-10X24 24.0000 10.0000 0.0000 0.0000 12.0000 0.0000
C2BG-12X12 12.0000 12.0000 0.0000 0.0000 22.0000 0.0000
GB-12X20 20.0000 12.0000 0.0000 0.0000 12.0000 0.0000
C1AG-12X12 12.0000 12.0000 0.0000 0.0000 15.0000 0.0000
C2AG-10X10 10.0000 10.0000 0.0000 0.0000 20.0000 0.0000
FB1234-12X15 15.0000 12.0000 0.0000 0.0000 12.0000 0.0000
FB2-10X18 18.0000 10.0000 0.0000 0.0000 12.0000 0.0000
FB5-12X23 23.0000 12.0000 0.0000 0.0000 12.0000 0.0000
C3AG-21X13 21.0000 13.0000 0.0000 0.0000 0.0000 0.0000
C3BG-23X15 23.0000 15.0000 0.0000 0.0000 0.0000 0.0000
C4BG-14X14 14.0000 14.0000 0.0000 0.0000 0.0000 0.0000
C4AG-12X12 12.0000 12.0000 0.0000 0.0000 0.0000 0.0000
C5BG-22X14 22.0000 14.0000 0.0000 0.0000 0.0000 0.0000
C5AG-20X12 20.0000 12.0000 0.0000 0.0000 0.0000 0.0000
F R A M E S E C T I O N P R O P E R T Y D A T A
SECTION TORSIONAL MOMENTS OF INERTIA SHEAR AREAS
FRAME SECTION NAME AREA CONSTANT I33 I22 A2 A3
C1BG-14X14 196.0000 5410.2536 3201.3333 3201.3333 163.3333 163.3333
FB1-10X24 240.0000 5905.2747 11520.0000 2000.0000 200.0000 200.0000
C2BG-12X12 144.0000 2920.3201 1728.0000 1728.0000 120.0000 120.0000
GB-12X20 240.0000 7212.4694 8000.0000 2880.0000 200.0000 200.0000
C1AG-12X12 144.0000 2920.3201 1728.0000 1728.0000 120.0000 120.0000
C2AG-10X10 100.0000 1408.3334 833.3333 833.3333 83.3333 83.3333
FB1234-12X15 180.0000 4434.0758 3375.0000 2160.0000 150.0000 150.0000
FB2-10X18 180.0000 3916.6705 4860.0000 1500.0000 150.0000 150.0000
FB5-12X23 276.0000 8920.3293 12167.0000 3312.0000 230.0000 230.0000
C3AG-21X13 273.0000 9454.5922 10032.7500 3844.7500 227.5000 227.5000
C3BG-23X15 345.0000 15404.0220 15208.7500 6468.7500 287.5000 287.5000
C4BG-14X14 196.0000 5410.2536 3201.3333 3201.3333 163.3333 163.3333
C4AG-12X12 144.0000 2920.3201 1728.0000 1728.0000 120.0000 120.0000
C5BG-22X14 308.0000 12165.5551 12422.6667 5030.6667 256.6667 256.6667
C5AG-20X12 240.0000 7212.4694 8000.0000 2880.0000 200.0000 200.0000
F R A M E S E C T I O N P R O P E R T Y D A T A
SECTION MODULI PLASTIC MODULI RADIUS OF GYRATION
FRAME SECTION NAME S33 S22 Z33 Z22 R33 R22
C1BG-14X14 457.3333 457.3333 686.0000 686.0000 4.0415 4.0415
FB1-10X24 960.0000 400.0000 1440.0000 600.0000 6.9282 2.8868
C2BG-12X12 288.0000 288.0000 432.0000 432.0000 3.4641 3.4641
GB-12X20 800.0000 480.0000 1200.0000 720.0000 5.7735 3.4641
C1AG-12X12 288.0000 288.0000 432.0000 432.0000 3.4641 3.4641
C2AG-10X10 166.6667 166.6667 250.0000 250.0000 2.8868 2.8868
FB1234-12X15 450.0000 360.0000 675.0000 540.0000 4.3301 3.4641
FB2-10X18 540.0000 300.0000 810.0000 450.0000 5.1962 2.8868
FB5-12X23 1058.0000 552.0000 1587.0000 828.0000 6.6395 3.4641
C3AG-21X13 955.5000 591.5000 1433.2500 887.2500 6.0622 3.7528
C3BG-23X15 1322.5000 862.5000 1983.7500 1293.7500 6.6395 4.3301
C4BG-14X14 457.3333 457.3333 686.0000 686.0000 4.0415 4.0415
C4AG-12X12 288.0000 288.0000 432.0000 432.0000 3.4641 3.4641
C5BG-22X14 1129.3333 718.6667 1694.0000 1078.0000 6.3509 4.0415
C5AG-20X12 800.0000 480.0000 1200.0000 720.0000 5.7735 3.4641
F R A M E S E C T I O N W E I G H T S A N D M A S S E S
TOTAL TOTAL
FRAME SECTION NAME WEIGHT MASS
C1BG-14X14 124.5905 0.3582
FB1-10X24 614.4574 1.7664
C2BG-12X12 2.4302 0.0070
GB-12X20 717.8785 2.0637
C1AG-12X12 423.8596 1.2185
C2AG-10X10 5.9066 0.0170
FB1234-12X15 0.0000 0.0000
FB2-10X18 438.8598 1.2616
FB5-12X23 0.0000 0.0000
C3AG-21X13 16.1251 0.0464
C3BG-23X15 3.8815 0.0112
C4BG-14X14 3.3077 0.0095
C4AG-12X12 5.6704 0.0163
C5BG-22X14 6.9304 0.0199
C5AG-20X12 33.0771 0.0951
C O N C R E T E C O L U M N D A T A
REINF CONFIGURATION REINF NUM BARS NUM BARS BAR
FRAME SECTION NAME LONGIT LATERAL SIZE/TYPE 3DIR/2DIR CIRCULAR COVER
C1BG-14X14 Rectangular Ties 16d/Check 3/2 N/A 3.0000
C2BG-12X12 Rectangular Ties 16d/Check 3/2 N/A 3.0000
C1AG-12X12 Rectangular Ties 16d/Check 3/2 N/A 2.0000
C2AG-10X10 Rectangular Ties 16d/Check 3/2 N/A 2.0000
C3AG-21X13 Rectangular Ties 16d/Check 3/3 N/A 2.0000
C3BG-23X15 Rectangular Ties 16d/Check 3/3 N/A 3.0000
C4BG-14X14 Rectangular Ties 16d/Check 3/3 N/A 3.0000
C4AG-12X12 Rectangular Ties 16d/Check 3/3 N/A 2.0000
C5BG-22X14 Rectangular Ties 16d/Check 3/3 N/A 3.0000
C5AG-20X12 Rectangular Ties 16d/Check 3/3 N/A 2.0000
C O N C R E T E B E A M D A T A
TOP BOT TOP LEFT TOP RIGHT BOT LEFT BOT RIGHT
FRAME SECTION NAME COVER COVER AREA AREA AREA AREA
FB1-10X24 2.0000 2.0000 0.0 0.0 0.0 0.0
GB-12X20 2.0000 2.0000 0.0 0.0 0.0 0.0
FB1234-12X15 2.2000 2.2000 0.0 0.0 0.0 0.0
FB2-10X18 2.1000 2.1000 0.0 0.0 0.0 0.0
FB5-12X23 2.3000 2.3000 0.0 0.0 0.0 0.0
Loading
The structures are analyzed with Alliance specification .
Seismic Loading
Proper structural design of any building structure must include loads due to earthquake shaking. Although there have been no major incident of earthquake hazard in the recent past of Bangladesh, earthquakes are not uncommon in this area. Scientific geological study of the earth crust below Bangladesh shows that Bangladesh does fall in moderate to high seismic risk zone. Statistical evidence from past major and minor earthquake incidents shows that a major earthquake is over due in the recent times of geological scale. Therefore it is necessary to prepare against any possible earthquake hazard. It should be kept in mind that the objective of earthquake resistance building design is not to make a strong building which can resist any damage due to earthquake. Instead, earthquake resistant design basically aims at minimizing the possible damage and casualty to an acceptable level.
Regarding the earthquake resistant design, it is essential to follow the specific design code. For the analysis and design checking of the building, Equivalent Static Force Method of BNBC (1993) is followed. The main considerations for calculation of earthquake load are given below.
Zone co-efficient, Z=0.15 (zone-2, Figure.6.2.10, BNBC, seismic zoning map of BNBC)
Structure importance co-efficient, I = 1.00 (Standard Occupancy, Table 6.2.23, BNBC)
Response modification co-efficient, R = 8.0 (IMRF, Table 6.2.24, BNBC)
Site co-efficient, S3 = 1.5 (type 3 soil as suggested in Table 6.2.25, BNBC)
In present model, using the parameters, Auto seismic load generated as per UBC94. Sample calculations are as follows-
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A U T O S E I S M I C U B C 9 4
Case: EX
AUTO SEISMIC INPUT DATA
Direction: X
Typical Eccentricity = 5%
Eccentricity Overrides: No
Period Calculation: Program Calculated
Ct = 0.03 (in feet units)
Top Story: STORY-3
Bottom Story: GF
Rw = 8
Z = 0.15
S = 1.5
I = 1
hn = 378.000 (Building Height)
AUTO SEISMIC CALCULATION FORMULAS
Ta = Ct (hn^(3/4))
If Z >= 0.35 (Zone 4) then: If Tetabs <= 1.30 Ta then T = Tetabs, else T = Ta
If Z < 0.35 (Zone 1, 2 or 3) then: If Tetabs <= 1.40 Ta then T = Tetabs, else T = Ta
V = Z I C W / Rw
C = (1.25 S) / (T^(2/3))
C <= 2.75
C >= 0.075 Rw, that is, C >= 0.6000
If T <= 0.7 sec, then Ft = 0
If T > 0.7 sec, then Ft = 0.07 T V <= 0.25 V
AUTO SEISMIC CALCULATION RESULTS
Ta = 0.3989 sec
T Used = 0.3275 sec
C Used = 2.7500
W Used = 6568.77
V Used = 0.0516W = 338.70
Ft Used = 0.00
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A U T O S E I S M I C U B C 9 4
Case: EY
AUTO SEISMIC INPUT DATA
Direction: Y
Typical Eccentricity = 5%
Eccentricity Overrides: No
Period Calculation: Program Calculated
Ct = 0.03 (in feet units)
Top Story: STORY-3
Bottom Story: GF
Rw = 8
Z = 0.15
S = 1.5
I = 1
hn = 378.000 (Building Height)
AUTO SEISMIC CALCULATION FORMULAS
Ta = Ct (hn^(3/4))
If Z >= 0.35 (Zone 4) then: If Tetabs <= 1.30 Ta then T = Tetabs, else T = Ta
If Z < 0.35 (Zone 1, 2 or 3) then: If Tetabs <= 1.40 Ta then T = Tetabs, else T = Ta
V = Z I C W / Rw
C = (1.25 S) / (T^(2/3))
C <= 2.75
C >= 0.075 Rw, that is, C >= 0.6000
If T <= 0.7 sec, then Ft = 0
If T > 0.7 sec, then Ft = 0.07 T V <= 0.25 V
AUTO SEISMIC CALCULATION RESULTS
Ta = 0.3989 sec
T Used = 0.3943 sec
C Used = 2.7500
W Used = 6568.77
V Used = 0.0516W = 338.70
Ft Used = 0.00
Wind Loading
Bangladesh is typically a storm prone area where due consideration to the thrust due to storm must be given in the analysis and design of building and structures. Wind load due to storm is typically modeled as lateral thrust force causing sway or overturning of the building. Detailed specifications on wind loading on buildings are outlined in BNBC (1993). The present project is located at Noljani, Chandana, Joydevpur, Gazipur. For which the following basic parameters are used in wind load calculation,
Basic wind speed, Vb= 133 mph
Exposure category = A
Structure Importance coefficient CI = 1.00
In present model, using the parameters, Auto seismic load generated as per UBC94. Sample calculations are as follows-
AUTO WIND EXPOSURE WIDTH INFORMATION (Exposure widths are from diaphragm extents)
STORY DIAPHRAGM WIDTH X Y
AUTO WIND CALCULATION FORMULAS
P = wind pressure = SUM(Ce Cq qs Iw) -- Method 1
Ce, the combined height, exposure and gust factor coefficient, is from UBC94 Table 16-G
qs is the wind stagnation pressure at the standard height of 33 feet
qs = 0.00256 V^2 >= 10 psf
AUTO WIND CALCULATION RESULTS
qs = 43.9322 psf
AUTO WIND STORY FORCES
STORY FX FY FZ MX MY MZ
STORY-3 (Forces reported at X = 0.0000, Y = 0.0000, Z = 450.0000)
0.00 0.00 0.00 0.000 0.000 0.000
STORY-2 (Forces reported at X = 0.0000, Y = 0.0000, Z = 324.0000)
0.00 0.00 0.00 0.000 0.000 0.000
STORY-1 (Forces reported at X = 0.0000, Y = 0.0000, Z = 198.0000)
0.00 0.00 0.00 0.000 0.000 0.000
GF (Forces reported at X = 0.0000, Y = 0.0000, Z = 72.0000)
0.00 0.00 0.00 0.000 0.000 0.000
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A U T O W I N D U B C 9 4
Case: WY
AUTO WIND INPUT DATA
Exposure From: Rigid diaphragm extents
Direction Angle = 90 degrees
Windward Cq = 0.8
Leeward Cq = 0.5
Top Story: STORY-3
Bottom Story: GF
No parapet is included
Basic Wind Speed, V = 131 mph
Exposure Type = B
Importance Factor, Iw = 1
AUTO WIND EXPOSURE WIDTH INFORMATION (Exposure widths are from diaphragm extents)
STORY DIAPHRAGM WIDTH X Y
AUTO WIND CALCULATION FORMULAS
P = wind pressure = SUM(Ce Cq qs Iw) -- Method 1
Ce, the combined height, exposure and gust factor coefficient, is from UBC94 Table 16-G
qs is the wind stagnation pressure at the standard height of 33 feet
qs = 0.00256 V^2 >= 10 psf
AUTO WIND CALCULATION RESULTS
qs = 43.9322 psf
AUTO WIND STORY FORCES
STORY FX FY FZ MX MY MZ
STORY-3 (Forces reported at X = 0.0000, Y = 0.0000, Z = 450.0000)
0.00 0.00 0.00 0.000 0.000 0.000
STORY-2 (Forces reported at X = 0.0000, Y = 0.0000, Z = 324.0000)
0.00 0.00 0.00 0.000 0.000 0.000
STORY-1 (Forces reported at X = 0.0000, Y = 0.0000, Z = 198.0000)
0.00 0.00 0.00 0.000 0.000 0.000
GF (Forces reported at X = 0.0000, Y = 0.0000, Z = 72.0000)
0.00 0.00 0.00 0.000 0.000 0.000
Load Combinations
The basic sources of loads are described in earlier section. These loads are applied on the model in seven basic categories. These are as follows:
Load Case 1: Self-weight of structure (SW), Floor finish and partition wall (SDEAD).
Load Case 2: Live load on roof (LL)
Load Case 3: Earthquake load on East-West Direction. (Ex)
Load Case 4: Earthquake load on North-South Direction. (Ey)
Load Case 5: Wind load on East-West Direction. (Wx)
Load Case 6: Wind load on North-South Direction. (Wy)
These four basic load cases are analyzed in ETABS-V9.7. The results are then combined in accordance with four specific combination categories as follows:
Load Combination as per Alliance Guideline Considering Live Load 42 Psf:
BNBC specifies a number of combination options. These are as follows:
Combination Case 1: 1.2 DL+1.6LL
Combination Case 2: 1.05 DL+1.275LL+1.0Wx
Combination Case 3: 1.05 DL+1.275LL-1.0Wx
Combination Case 4: 1.05 DL+1.275LL+1.0Wy
Combination Case 5: 1.05 DL+1.275LL-1.0Wy
General
As described earlier, the whole process is done in several phases. At first field survey is performed. Then structural design is reviewed. Then gathered information is analyzed together. Output of analysis is reviewed in two categories. One is strength, another is serviceability. These are briefly described below:
Present Loading condition:
At present (while visual inspection is done & recorded), the building is using for several process like knitting, sewing and several process. Operating load includes weight of machine, some furniture, and some co-lateral loads suspended from ceiling, raw materials & operator’s weight. Live load does not exceed 1.0 kN/ sq.m.
Review of Structural Strength:
For analytical investigation 3D full scale model is prepared with Etabs. Member forces are taken from analysis & design is evaluated with BNBC as well as ACI Code. Forces Main features are described below:
Column:
From the analysis it is seen that almost all columns are in very good condition. No over stressed columns are found in any of the Combination Categories. Actually Combination Category is standard category as per BNBC2006. When a structure or any of its part cannot comply Combination Category-I, then step by step downward categories are evaluated. Since, this structure is capable enough to sustain any loading under Combination Category-I, it is not required to evaluated for other Combination Categories.
Assumptions /Considerations:
Support system is considered fixed.Slab on grade is considered as load transferring medium.
All structural members are rigidly connected at joints for welding connection.
In-fill brick wall has no contribution on rigidity for out of plane loading.
Continuous lintels are considered as structural element.
Small dislocations of members are not taken account.
The following two loading conditions are considered a) Gravity load b) gravity along with lateral load
Conclusion:
The capacity of existing reinforced concrete structure has been evaluated. Under the evaluation standard procedure is step-by-step followed. Following things are found in present study
a) Building Assessment dimension & grid dimension are verified, in field dimension are found almost correct with a little variation. In analysis average dimension are taken. Those are also presented in as built drawing.
b) All columns dimension are verified and the verified corrected column dimension are used in the analysis and presented in the as build drawing.
c) Column reinforcement information was not present in construction document. It is gathered through site interview of Building Assessment owner & construction people. Finally it is verified through rebar scan report and by exposing the concrete cover. We got several types of reinforcement arrangement & quantity in similar types of columns. From that information we found little variation of rebar provided. We consider minimum reinforcement for maximum safety in the analysis.
d) MAK CONSULTANTS Engineers checked a number of columns of the building from ground floor up to roof. Columns, which are the main vertical and load bearing component of a building has no sign distress or cracking anywhere in the building. The column faces are almost well and some minor noticeable points that should be mentioned are the quality of construction.
e) A number of beams building from ground floor up to roof checked and closely observed the condition with technical aspects. Beam, which the slab load is bearing component of a building. The beam size is found same as the construction drawing.
f) All slab panels were checked and it is two way slabs consisting of 6.0 inch thickness (with a little deviation in few places).
g) Foundation checked by excavating earth up to bottom of footing and found grade beams in proper level. Footing size, depth and shape properly measured and found no signs of distress or crack. Grade beams also thoroughly inspected and found no cracks or distress.
h) Reinforcement & concrete strength of footing are not verified.
i) It was not possible to verify top reinforcement of floor beams. Provided data is taken from site interview.
j) Considering the above things & from analysis it is seen that all columns as well as other members are safe under present loading.
Recommendation:
Based on the above findings and conclusions, the following recommendations are suggested for the structure:
(1) In order to get smooth service from the structure and to enhance service al life, it is recommended to monitor structural health periodically and keep under proper maintenance. For owners or responsible authorities, it is recommend taking the periodical measurement of time variant measures like displacement, strains and stresses, damage evaluation (e.g. crack width) and vibration characteristics with the aim to detect changes in the structural properties and in some cases to be alarmed, when limit states are reached or exceeded.
(2) In order to get smooth service & enhance the service life of the structure following things are recommended -
o Strictly following load plans.
o Do not change the uses of floors for Building Assessment
o Do not store heavy materials in a bulk volume at a single panel.
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