Seismic Vulnerability Assessment and Retrofit Design of Heritage Buildings of Kathmandu Valley Kirti TIWARI 1, Hima SHRESTHA 2 and Ramesh GURAGAIN 3 1

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1 Seismic Vulnerability Assessment and Retrofit Design of Heritage Buildings of Kathmandu Valley Kirti TIWARI 1, Hima SHRESTHA 2 and Ramesh GURAGAIN 3 1 Structural Engineer, National Society for Earthquake Technology-Nepal, Nepal ktiwari@nset.org.np 2 Director, Earthquake Engineering Research and Training Division, National Society for Earthquake Technology-Nepal, Nepal 3 Deputy Executive Director, National Society for Earthquake Technology-Nepal, Nepal ABSTRACT There are many cultural heritage buildings in Nepal made of burnt clay brick in mud mortar dated more than 100 years of age. Considering the high seismic hazard of Nepal preservation of its architectural and archeological values is very important. This paper focuses on seismic vulnerability assessment and retrofit design of one of such historic buildings Keisar Mahal carried by NSET just few months before the Gorkha Earthquake. Although the principles for evaluating the historic structures are similar to those for other buildings, the comprehensive assessment plan was prepared to study the special condition and considerations that existed in historic buildings of Rana period in Nepal. Different detailed non- destructive and intrusive tests were carried out in the building to find the condition and properties of materials used. Detail structural analysis shows that the critical vulnerable factor is large out-of-plane moments at higher intensities of shaking. Out of various alternatives of seismic strengthening, adding of some cross walls and buttresses and increasing the rigidity of floors by means of bracing are effective means to reduce out-of-plane moments. Similarly, steel plates are suggested to resist in-plane stresses: at critical locations near jambs of door/window openings and corners with spacing limiting to 1m-1.2m. Keywords: historic building, Rana building, seismic assessment, retrofitting 1 DESCRIPTION OF HERITAGE BUILDING UNDER STUDY Kaiser Mahal is a Rana Palace in Kathmandu built in 1895 by Chandra Shamsher Jung Bahadur Rana for his son Kaiser Shamsher Jung Bahadur Rana. It is one of the historic durbars of Kathmandu with Neoclassical architecture. Such Rana palaces are made of burnt brick in mud mortar with lime plaster and arresting French windows. They have Grecian columns and four wings with a large courtyard in middle for religious and ceremonial purposes, so is Kaiser Mahal. It has a courtyard in the middle with projected wings at the South-East and South-West portion. The building is three stories at East, South and North portion, the original structure and four storey at West portion which was added later. Wall thicknesses are in the range of 900mm, 850 mm, 650 mm, 600 mm, 550 mm, 500 mm, 450 mm, 350 mm and 250 mm, mostly thick walls in first three stories. Floor/roof structures are made of Jack Arch and timber flooring.

2 Fig 1: Front View of the Building Fig 2: Building Foot Print 2 VISIBLE PHYSICAL CONDITION OF THE BUILDING BEFORE GORKHA EARTHQUAKE From the inspection of the building, visible cracks were found on the walls of the building at many locations. Near the North-West and North-East corners of the building there were large vertical cracks throughout the walls and floors initiated from the ground floor walls to the roof level of the building. However, there was no crack seen in plinth level of the building and below. Crack width increases from average of 1.0 mm at ground floor level to 5-10 mm and more at roof level. The nature of crack indicates it may be due to settlement. The settlement could have been occurred as a result of improper drainage and leakage leading to foundation erosion and subsequent crack in upper parts of the building which is further aggravated due to vibration in the building. Similarly, there were several vertical and diagonal minor cracks above the door/window openings. This is more likely due to the difficulty in load transfer on the wall due to the presence of openings and degradation of material strength with time. In addition, there were leakages in the building from toilets and water and sanitary pipelines, which made the wall damp resulting in decay of wood structures and growth of lichen and trees on the walls. 3 FIELD INVESTIGATIONS AND OBSERVATIONS Field investigation was carried to verify the details at site and to determine the actual condition and strength of different structural elements. This was done by visual observation, non-destructive and intrusive tests such as foundation exploration, making inspection holes on walls, in situ inplane shear test, micro tremor test, wood decay test and flat jack test. 3.1 Inspection Hole on Walls Brick lay pattern is an important parameter to determine the integrity of brick masonry wall. An opening of size 450mm x 450mm x450mm were created at two places, and observed the brick lay pattern. It was found that walls are constructed using burnt clay brick in mud mortar. Average thickness of mortar is 10 mm. All bricks are laid properly with offset along the length and breadth of the wall as in English bond

3 3.2 In Situ In-plane Shear Test It provides a direct measurement of the shear resistance of mortar joints in masonry. The test locations were prepared by removing the brick, including the mortar, on one side of the brick to be tested. The head joint on the opposite side of the brick to be tested was also removed. With care that the mortar joint above or below the brick to be tested was not damaged. The hydraulic ram was inserted in the space where the brick was removed. A steel loading block was placed between the ram and the brick to be tested so that the ram will distribute its load over the end face of the brick. The dial gauge was inserted in the space. The brick was then loaded with the ram until the first indication of cracking or movement of the brick. The ram force and associated deflection on the dial gage were recorded. Twenty Six test locations, at least one location at each wing each floor, were selected based on different wall thickness, internal and external locations. The test was carried out at 13 locations at ground floor, 7 locations at first floor and six locations at second floor. From the observation, final corrected shear strength of brick masonry is obtained as per ASTM standard and IITK- GSDMA Guideline and the corrected shear strength obtained are N/mm 2 and N/mm 2 respectively. The difference in these values from two standards, ASTM and IITK-GSDMA Guideline, is due to the coefficient of friction between the brick and mortar that is assumed as per the site condition. Lower value N/mm2 is used for design purpose. Fig 3: Inspection Hole on Wall Fig 4: In-situ In-Plane Shear Test 3.3 Micro-tremor Test Micro Tremor measurements were taken to calibrate the numerical computer analysis. The Micro Tremor measurements were obtained at 18 locations in second floor and 1 location in first floor. As far as possible, measurements were taken at four corners and near CG of second floor of all four wings of courtyard building. The average fundamental frequency in East-West (X) direction was found to be 2.56 Hz, while in North-South (Y) direction was 2.74 Hz. The fundamental time period at X and Y-directions was found to be 0.39 sec and 0.36 sec respectively. Despite their thick walls, the fundamental time period is slightly higher, this may due to the cracks on walls, flexibility of floors or insufficient bracing of walls. 3.4 Wood Decay Test

4 Timber is extensively used in different forms in the building. Its current condition is very important parameter during the assessment of the building. Besides inspecting the surface visually, the condition of wooden members: beams, girders, rafters, posts, windows, doors, etc were tested with the help of decay detection instrument, IML PD Series. During the test, a drilling needle with a diameter of 1.5mm and 3 mm cutting tip is inserted into wood under constant drive. While drilling, the resistance was measured as a function of drilling depth of the needle. The data was plotted on a scale 1:1 simultaneously. The high amplitude graphs represent the higher intact of wood. The test was carried out only on the exposed wood surface at 86 different locations. From the observation, except few beams most of the wooden members are of good quality. Fig 5: Microtremor Test Fig 6: Wood Decay Test 3.5 Flat Jack Test Flat jack testing is the direct and in-situ testing method to determine the local compressive and stress-strain behavior of the masonry and requires only the removal of portion of mortar from the bed joints. This test is intrusive since the damage is temporary and can be easily repaired after testing. Flat jack testing was carried as per ASTM Standards (ASTM C1196 and ASTM C1197) by using two flat jack plates of size R-6-16 (0.15 X 6 X 16 ). Two slots of size 6.5 x 17 were prepared at 18.5 apart (5 layers of brick) and gauge point pairs were selected to measure the deflection of the masonry units. Flat jacks were then introduced into both slots, and the initial distance between gauge points were measured. By pressuring the flat jacks, loads applied to the wall specimen. With a pressure increase in the flat jacks, the distance between gauge point pairs decreased. By gradually increasing the pressure, the pressure and deformation were recorded and stress-strain curve was developed. The pressure was increased till there was failure in the masonry specimen. From the three different flat jack tests the average value of Modulus of Elasticity of Masonry and Compressive Strength of Masonry was found to be N/mm 2 and 1.21 N/mm 2 respectively. 3.6 Brick Test Three brick samples were taken from the building wall, compressive strength and water absorption test was carried out at Central Material Testing Laboratory, Institute of Engineering, Nepal. The

5 average breaking strength of brick was found to be N//cm 2 and water absorption of three samples are 14.29%, 15.62% and 18.76%. Fig 7: Flat Jack Test Fig 8: Brick Test 4 DETAIL STRUCTURAL ANALYSIS Finite Element Modeling of the Kaiser Mahal building was done using structural analysis and design software program, SAP 2000 Advanced For simplicity, only the west portion of the courtyard was modeled (red rectangular mark on building plan). Load bearing brick masonry walls were modeled as single layered shell elements. Since the flooring of the building is made of brick and mud with timber girders, only the main timber girders were modeled. Seismic coefficient method was used to analyze the building. Indian Seismic Code IS 1893:2002 was used for lateral load calculation and seismic coefficient value was also compared with the Nepal National Building Code NBC 105: D view of the SAP model is shown below. Fig 9: 3D model of West Portion of the Kaiser Mahal Building in SAP2000

6 Storey Height (m) In-plane and out-of-plane stresses are studied. From the analysis, large amount of out of plane bending moments are produced on the walls due to the large span of wall, height of the building and flexible floor diaphragm. While in-plane stresses are also not to be ignored. 5 CONCEPTUAL RETROFIT STRATEGY Since the building is a national heritage, preservation of architectural and archeological value is vital. The main strategy of seismic strengthening is to intervene as less as possible. The proposed strategy to bring the building performance within the acceptable level of life safety are i)addition of internal buttresses and cross walls to reduce the span of the wall, ii) Increase floor rigidity and iii) Addition of tension resisting members on the piers Some cross walls and buttresses are added on second and third floor of the building to reduce the out-of-plane moments of load bearing walls. Similarly, floor bracings are added to improve the rigidity of floor diaphragm. Modified building plan significantly reduces out-of-plane bending in walls both horizontally and vertically and also the building deformation (See fig 10). Further to improve the integrity and ductility in the building and also to resist tension force in the wall panels vertical tension resisting elements, Splints of steel straps are introduced at corners and junction of walls and at jambs of door/window openings; Horizontal bands of tension resisting element of steel straps, are provided at lintel and floor levels. Schematic sketch is shown below (Fig 11 & 12): After addding Buttresses, cross walls and floor bracing existing building Maximum Deformation (mm) Fig 10: Comparison of Out-of-plane Deformation of the West Portion due to Earthquake Loading

7 Fig 11:Wall Elevation showing Metal Plates used as Vertical Splints and Horizontal Bands Fig 12: Wall Plan with Metal Plate as Vertical Splints and Horizontal Bandages

8 6 DAMAGE TO THE BUILDING IN GORKHA EARTHQUAKE 2015 AND WAY FORWARD The detail damage assessment and retrofit design of the building was done just before the Gorkha Earthquake 2015 and implementation was yet to be taken. The building is further damaged due to the Gorkha earthquake Rapid visual damage assessment indicates the building has suffered moderate structural damage with minor and major shear and flexural cracks at many locations which would require more repair works. The building having historical and cultural value, it is very necessary to maintain and strengthen the building structure to preserve the value of its time though the cost of intervention is slightly high. For this, a detail damage assessment along with the appropriate retrofit scheme is necessary to safeguard the building with national importance. REFERENCES NSET [2015] A report on Seismic Vulnerability Assessment and Retrofit Design of Kaiser Mahal Building Dr. Rai, D.C. [2005] IITK-GSDMA Guidelines for Seismic Evaluation and Strengthening of Buildings: Provisions with Commentary and Explanatory Examples, IIT, Kanpur Varum, H. et al. [2006] Seismic Evaluation of Old Masonry Buildings: Performance and Strengthening, Paper 85, Proceeding of the Eighth International Conference on Computational Structures Technology, Civil-comp Press, Stirlingshire, Scotland. Romeu Vicente et al. [2011], Evaluation of strengthening Techniques of Traditional masonry buildings: Case Study of a Four Building Aggregate, Journal of Performance of constructed Facilities ASCE/May/June/2011 Department of Archeology [1998] An Assessment of the Structural Condition of 55 Windows Palace, Durbar Square, Bhaktapur Investigation Team s Report Volume 1, Kathmandu. Ceroni Francesca et al. [2012] Assessment of Seismic vulnerability of a historic masonry building, Buildings 2012, 2, ; doi: /buildings Look W. David et al. [1997] The seismic retrofit of historic buildings: Keeping preservation in the forefront, US Department of the Interior, National park service cultural resources, heritage preservation services. ASTM C [2013] Standard Test Method for In Situ Deformability Properties Using Flat Jack Measurements, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, US ASTM C (2013) Standard Test Method for In Situ Compressive Stress Within Unit Masonry Estimated Using Flat Jack Measurements, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, US ASTM C (2011) Standard Test Methods for In Situ Measurement of Masonry Mortar Joint Shear Strength Index, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, US RILEM MDT.D.4 [2004] In-situ Stress Tests based on the Flat Jck, RILEM TC 177-MDT: Masonry Durability and On-site Testing, Material and Structures, Vol. 37. RILEM MDT.D.5 [2004] In-situ Stress-strain Behavior Tests Based on the Flat Jack, RILEM TC 177-MDT: Masonry Durability and On-site Testing, Material and Structures, Vol. 37.