Furthermore, the proposed scheme does not alter the natural features and aesthetics of the URM buildings. It was found that the proposed discretization method predicts the lateral strength and crack pattern development of URM buildings with higher accuracy.
A CKNOWLEDGEMENT
Experimental Study on Strengthening of URM Buildings 89
Estimation of Lateral Strength of URM Building 111
Homogenized Discretization Method for Numerical Simulation of
L IST OF T ABLES
Lateral load testing of Wall 1: (a) load arrangement and crack formation and (b)(c) close-up of the crack propagation at the bottom. Damage observed in different walls during lateral load testing of the reinforced building 2 (Model 2): (a) Walls 2 and 3*, and (b) Wall 3.
L IST OF S YMBOLS
I NTRODUCTION
- O VERVIEW
- T YPES OF M ASONRY B UILDINGS IN I NDIA
- Unreinforced Brick Masonry with Reinforced Concrete Slab
- Unreinforced Brick Masonry with Pitched Clay Tile Roof
- Unreinforced Brick Masonry with Timber Roof
- Unreinforced Brick Masonry with GI Sheet Roof
- Seismic Vulnerability of Unreinforced Brick Masonry Buildings
- B EHAVIOR OF URM B UILDINGS D URING P AST E ARTHQUAKES
- Bhuj, Gujarat Earthquake, 2001
- North Kashmir Earthquake, 2005
- Sikkim Earthquakes, 2006, 2011
- Varzaghan-Ahar twin Iran Earthquakes, 2012
- Christchurch Earthquakes, 2010, 2011
- Nepal Earthquake, 2015
- Common Observations
- S TRENGTHENING OF URM B UILDINGS
- S COPE AND O BJECTIVES OF THE P RESENT S TUDY
- O RGANIZATION OF THE T HESIS
URM buildings with reinforced concrete (AB) slab can be found in all parts of the country. The improvement of the lateral load behavior of reinforced buildings was evaluated based on an experimental study.
L ITERATURE R EVIEW
- O VERVIEW
- B EHAVIOR OF URM W ALLS S UBJECTED TO L ATERAL L OADING
- In-Plane Behavior of Masonry Walls
- Out-of-plane Behavior of Masonry Walls
- B EHAVIOR OF URM B UILDINGS S UBJECTED TO L ATERAL L OADING Although numerous experimental studies were carried out in the past on individual URM
- Gap Areas
- S TRENGTHENING OF URM B UILDINGS
- Indian Code Provisions: Design and Strengthening of Masonry Buildings In India, some design codes are available that provide guidelines to improve the seismic
- Gap Areas
- S UMMARY AND I DENTIFIED G AP A REAS
Further in-depth research on the influence of openings on the in-plane wall strength should be conducted. Such research can increase the effectiveness of the seismic design of the wall components in the building.
P RELIMINARY N UMERICAL I NVESTIGATION
- O VERVIEW
- N UMERICAL M ODELLING
- Strand7 FE Code
- Abaqus FE Code
- SAP2000 Equivalent Frame Approach
- B UILDING G EOMETRY AND FE D ISCRETIZATION
- N ON - LINEAR A NALYSIS AND R ESULTS
- Numerical analysis of URM building
- Strengthening Scheme #1: Steel Bands at the Lintel Level
- Strengthening Scheme #2: Steel Bands at Lintel and Sill Level
- Strengthening Scheme #3: Horizontal Steel Bands at Lintel and Sill Level and Vertical Steel Bands around the Openings
- S ENSITIVITY A NALYSIS V ARYING T HICKNESS AND W IDTH OF THE
- D ESIGN E QUATIONS FOR E STIMATION OF C APACITY
- I NFLUENCE OF O PENINGS IN M ASONRY B UILDING
- Influence of only External Bands and Combination of External and Internal Bands
- S UMMARY
The geometry of the building and the dimensions of the walls (steps, lintels and piers), as well as the dimensions of the openings (windows and doors) are fully defined in Figure 3.4 and Table 3.4. In the preliminary study, the steel strips were mounted only on the outer face of the walls. Stress contour on the 4 sides of the building due to the application of steel bands at the architrave level.
The maximum increase in the lateral load-bearing capacity of the URM building is observed (ranging from 75% to 83%) when it is strengthened using scheme #3.
E XPERIMENTAL S TUDY ON URM W ALLS
- O VERVIEW
- T ESTS ON M ASONRY C ONSTITUENTS
- Compressive Test on Bricks
- Compressive Test on Mortar
- Triplet Shear Test
- Tensile Bond Test
- Compressive Test on Masonry Prism
- E XPERIMENTAL E VALUATION OF URM WALLS
- Experimental Results
- S UMMARY
A small bed joint crack was also observed at the top of the wall specimen at an offset of 6 mm (Figure 4.9a). Lateral load testing of wall 1: (a) load distribution and crack initiation and (b) (c) close-up view of crack propagation at the bottom of the wall. Lateral load testing of wall 3: (a) crack along the entire length of the wall at the bottom at the displacement level of 12 mm and (b) a close-up view of the crack formed at the bottom of the wall.
The crack developed much later than the flexural crack at the bottom of the wall.
E XPERIMENTAL S TUDY ON S TRENGTHENING OF
URM B UILDINGS
O VERVIEW
It was then retrofitted with steel strapping running the length of the building at various levels. The second building was reinforced with horizontal steel ties along the entire perimeter of the building, only at the lintel level (Figure 5.1b). While the third building was reinforced using horizontal steel ties at the lintel and sill levels along the entire perimeter of the building.
The steel bands were mounted both externally and internally on the surface of the walls and connected using steel bolts.
E XPERIMENTAL S ETUP
Overview of URM building specimens: (a) Unreinforced URM building (denoted as URM), (b) building strengthened using horizontal steel bars at deck level (denoted as Model 1), and (c) building reinforced using horizontal steel strips at the sill and archway levels and vertical strips adjacent to the openings (marked as Pattern 2). Experimental setup: (a) Plan and (b) Elevation of building showing loading arrangement, sensors and wall openings. A thick brick parapet wall 0.9 m high was also built on top of the slab above the walls.
Four LVDTs were connected to four plate corners to capture the rotation of the building in the plan due to asymmetrical wall configurations (Figure 5.2a).
T ESTING OF URM B UILDING (U NSTRENGTHENED )
Continuous cracks in the lintel level along the perimeter of the building caused the upper part of the building to begin to sway. During the test, a mixed failure mechanism consisting of shear and tensile failure in the masonry was observed, along with a torsional response of the specimen at higher displacement rates, as shown in Figures 5.7 and Figure 5.8. The hysteresis curves and the cumulative energy dissipation capacity of the sample obtained during the test are shown in Figure 5.9a and Figure 5.9b, respectively.
The hysteresis curves show that the lateral load bearing capacity of the URM specimen is about 88 kN.
T ESTING OF S TRENGTHENED B UILDING 1 (M ODEL 1)
During the lateral load tests, shear and tensile strength failure in the masonry appeared to be the main reason for the failure of the reinforced building 1. It can be seen that the use of a layer of steel strapping at the lintel level did not provide any significant improvement. in the lateral load-bearing capacity of the URM building. Similar to the URM building, the lateral load-bearing capacity of Model 1 also started to deteriorate suddenly after reaching the maximum value, as shown in the envelope curve of Figure 5.14a.
Lateral load response of reinforced specimen (Model 1): (a) hysteresis curves and capacity envelope, and (b) cumulative energy dissipation capacity.
T ESTING OF S TRENGTHENED B UILDING 2 (M ODEL 2)
The test was closed at the displacement level of 30 mm to avoid complete failure of the walls. LVDTs were used to record this rotational movement of the RC plate of all specimens as shown in Figure 5.2a. Damage observed in different walls during lateral load testing of reinforced building 2 (Model 2): (a) Walls 2 and 3*, and (b) Wall 3 and 1*.
This means that the steel bands contribute significantly to the lateral load resistance and delay the formation of cracks and failure in the walls of the building.
S UMMARY
Therefore, a more refined numerical simulation of the strengthened URM buildings will be performed in the next chapter. It was observed that provision of a single steel band at lintel level on both sides of all the walls of the URM building (Model 1) did not result in any significant increase in its lateral load-bearing capacity. Therefore, another strengthening scheme was adopted (model 2), where the steel bands were provided both at lintel and frame level on both sides of all the building's walls.
In addition, vertical steel bands were also provided around openings on both faces of the walls.
E STIMATION OF L ATERAL S TRENGTH OF URM
B UILDING
- O VERVIEW
- N UMERICAL S TUDY OF URM WALLS
- Numerical Results 1. Wall 1
- N UMERICAL S TUDY OF URM B UILDINGS
- A NALYTICAL E VALUATION
- Lateral Strength of URM Walls 1. In-Plane Resistance of Walls
- Lateral Strength of URM Building
- S UMMARY
- H OMOGENIZED D ISCRETIZATION M ETHOD FOR
The capacities of the individual walls were then methodically combined to estimate the lateral strength of the URM building. Therefore, adopting this method may also overestimate the OOP strength of the wall. Analytical evaluation of the out-of-plane strength of URM walls in kN Wall Griffith &.
The rest of the lateral resistance is provided by the box action in the URM building.
N UMERICAL S IMULATION OF URM B UILDING
G ENERAL
This chapter discusses a numerical simulation procedure that provides a fast and reliable tool for accurate predictions of the seismic response of URM structures. The idealization of the Equivalent Frame, which was probably first introduced by Magenes and Fontana (1998), was characterized by an extreme simplification of the problem. The piers and spans were modeled by placing non-linear springs at the two ends of the masonry elements to capture the bending behavior and displacement at the center.
Although the approach provides a good estimate of lateral load resistance and prediction of the failure.
N UMERICAL S IMULATION OF URM B UILDING 1. Numerical FE Modelling Strategies
- Results
Lateral load behavior for wall 1: (a) Experimentally observed response, (b) Capacity curve comparison of the numerical models with experimental specimen, (c) Damaged model of commonly used homogenized model and (d) Damaged model of the proposed homogenized model. Lateral load behavior of wall 2: (a) Experimentally observed response, (b) Capacity curve comparison of the numerical models with experimental specimen, (c) Damaged model of commonly used homogenized model and (d) Damaged model of the proposed homogenized model. The lateral load response of the specimen again exhibited a mixed failure mode of flexural and sliding shear type as shown in Figure 7.8a.
Lateral load behavior of wall 3: (a) Experimentally observed response, (b) Performance curve comparison of numerical models with experimental sample, (c) Damaged model of the commonly used homogenized model, and (d) Damaged model of the proposed homogenized model.
N UMERICAL S IMULATION OF S TRENGTHENED URM B UILDING
The strengthened URM model taking into account the nodal connection of type 4 was further analyzed to study the influence of the cross-sectional area of steel faces on the lateral strength of the URM building. The numerical simulation was performed on the strengthened URM building model by varying the cross-sectional area of the steel flats based on the sizes of the steel faces available in the market. The simulation results showed a slight increase in the lateral strength of the building with an increase in the cross-sectional area of the steel faces.
However, the increase became less significant at higher cross-sectional areas of the steel flats.
S UMMARY
Regression analysis of the numerical results was performed to develop an empirical equation to estimate the lateral strength of the building as a function of aspect ratio, wall thickness and tensile strength. Further numerical simulations were performed on a URM building strengthened with horizontal and vertical surface-mounted steel planes by varying the cross-sectional area of the steel planes. Therefore, it is not recommended to provide higher cross-sectional areas of the steel straps.
S UMMARY AND C ONCLUSION
- O VERVIEW
- S UMMARY
- Preliminary Numerical Investigation of URM buildings
- Material Characterization and Experimental Evaluation of URM Walls In this part of the study, the mechanical properties of the masonry used to construct the
- Experimental Evaluation of a Strengthening Scheme for URM Buildings Numerous past studies have revealed that steel members can be economically and
- Numerical and Analytical Study for Estimation of Lateral Strength of URM Buildings
- Development of Homogenized Discretization Method for Numerical Simulation of URM Building
- C ONCLUSIONS
- R ECOMMENDATION FOR F UTURE W ORK
Higher values of the cross-sectional area of the ties did not contribute much to an increase in the lateral strength of the URM building. The size of the steel bands was kept the same throughout the experimental study: 40 mm × 5 mm. Therefore, the inconsistency of the available analytical methods in estimating the lateral strength of URM walls was highlighted in this study.
The empirical equation developed can easily be used to estimate the potential increase in lateral strength of URM buildings due to the suggested strengthening scheme.
R EFERENCES
Indian Standard Code of Practice for Preparation and Use of Masonry Mortars.” IS 2250, New Delhi, India. Indian Standard Methods of Testing Burnt Clay Bricks—Part 1: Determination of Compressive Strength.” IS 3495, New Delhi, India. Code of practice for design loads (other than earthquake) for buildings and structures.” IS 875 (Part 1), (New Delhi, India).
Comprehensive Numerical Approaches for Design and Safety Assessment of Steel Strap Retrofit Masonry Buildings in Developing Countries: The Case of India.” Building and Construction Materials, Elsevier Ltd.
