Samuel Pendreigh

2017 ASSIGNMENT 2 Structural Assessment of the Tramway Hotel BILD 322 - STRUCTURES SAMUEL PENDREIGH - | 28/09/2017 Contents Introduction ....................................................................................................................................... 2 History ............................................................................................................................................... 2 Structural Description ........................................................................................................................ 2 Foundations ................................................................................................................................... 2 Exterior Facades ............................................................................................................................. 2 Internal Partitions .......................................................................................................................... 2 Diaphragms and Roof ..................................................................................................................... 2 Garage ........................................................................................................................................... 2 Kitchen/Restaurant ........................................................................................................................ 2 Ground Floor Plan and Force Diagrams .............................................................................................. 3 Resistance to forces ........................................................................................................................... 3 Modelling .......................................................................................................................................... 5 Assumptions .................................................................................................................................. 5 Initial Results.................................................................................................................................. 5 Recommended Action........................................................................................................................ 5 Option 1 ......................................................................................................................................... 5 Option 2 ......................................................................................................................................... 5 Conclusion ......................................................................................................................................... 6 References ......................................................................................................................................... 6 Appendices ........................................................................................................................................ 7 Introduction The following report assess the structural stability of the Adelaide Road Hotel located at 114 - 116 Adelaide Road and 15-17 Drummond St, Newtown Wellington. The building has been run through RESIST to create a 100% Earthquake NBS (New Building Standard) in terms of a retrofit. Currently the building is a WCC Heritage Building and has received a 124 Notice. Recent Retrofitting has occurred which only brings the building to 33% NBS. History The building was built in 1899 with the proposal approved on the 17th of January. The building was of pressed brick construction with concrete foundations. All of the internal structure including the floor boards, rafters ceiling joists, partitions etc were of Rimu or Matai construction (See Appendices – Figure 5 and 6 – for a schematic representation) Structural Description Foundations      Foundations and Floors were originally constructed of Portland cement and Bluestone. Timber floor has been removed and a 100mm Concrete slab has been poured over the existing slab with 16mm tie bars placed in the slab. HY60 steel is used to reinforce the foundation. Beam ties connect the Steel beams. Steel hairpin ties reinforce the Columns. 400mm ᶲ Augured holes 1200mm down filed with stanchion steel columns (150UC150) Exterior Facades    The North, West and South of the building are of reinforced concrete. The East Façade is combination of 200mm reinforced concrete masonry and brick. Reinforced with 31mm B.W gauge hoop iron. Internal Partitions    Both 90mm timber framing lined with brace line GIB and reinforced concrete block and brick. GIB brace Precast In-Situ concrete panel has been attached to the west wall at the main entry point to reinforce current construction Diaphragms and Roof   Cedar Diaphragms are located on the second floor. A concrete Bond beam lines the roof which secures the parapets to the existing brick walls with steel rods and stirrups. First floor is CWB concrete forming a rigid diaphragm able to transfer torsion. Garage    Garage area has added 250UB31 Columns and Beams to create a portal frame with 6mm stiffeners and 75x75x4mm struts. Steel frames which line the West wall of the garage are 150x75 channel with 64x65x4 RHS beams bolted to the floor with 2x16mm ᶲ bolts. 16mm ᶲ steel tension only braces are welded to the RHS and Channel. The original (still existing) ground floor plan for the main building (not stables or shops – now the garage) is a 130mm thick concrete slab reinforced with 665L HRC mesh and with Beams for lateral stability. Kitchen/Restaurant   100mm tick topping slab with D16 ties to stanchions Same Portal frame erected in stage area as in Garage area - 250UB31 Columns and Beams to create a portal frame with 6mm stiffeners and 75x75x4mm struts. Ground Floor Plan and Force Diagrams Figure 1 Ground Floor Plan of Vertical Structural Elements and the C.O.M and C.O.R Figure 2 Ground Floor Plan Detailing Vertical Structural Elements and the C.O.M and C.O.R The C.O.M (Centre of Mass) for the structure remains central due to the concrete walls being evenly spaced from West to East. The C.O.R (Centre of Rigidity) however has been moved to South Eastern corner of the structure due to there being a greater amount of stiffness in that area from the tightly grouped concrete block walls and columns. Resistance to forces Torsion occurs when the centre of rigidity is not at the same location as the centre of mass. The following, Figure 4, is a diagram depicting how the tramway hotel is effected by an applied force. The roof diagram will act similar to a simply supported beam (See Figure 4). In its Y-Direction (The Transverse Direction) the diaphragm will receive inertia forces and transfer them to the columns and floors meaning that shear forces will be a maximum at the ends of the diaphragm (either end of the longitudinal direction). This also means that in the direction to which the diaphragm receives the force will cause the diaphragm to resist in compression and tension on the furthermost side of the applied force (See Figure 4). In the case of the Tramway Hotel as the COR and COM are not equal torsion will occur due to the shear force not all being distributed laterally. Figure 3 demonstrates the effects of the torsion upon the building when a force is applied either along the transverse (in plane) or longitudinal (out of plane) axis (Miranda, 2012). The assessed buildings ability to resist torsion in the roof is currently lowered as it has not been tied to the structural walls. There is also a void in the diaphragm for two stair cases and a lift shaft meaning that a trim beam should be added to reduce the amount of flexure (Scarry, 2014). The buildings ability to resist torsion is at a better within the first floor as it is constructed form concrete which increases its rigidness, however it too is susceptible to the problems that the voids place upon the building in terms of lowering flexure. Figure 3: Shear force diagram depicting torsion Figure 4: Plan view of a UDL's effects on the roof diaphragm Figure 4 demonstrates the expected BMD, SFD and displacement/deformation from the roof diaphragm when a load is applied perpendicular to its length. As stated before a diaphragm works by transferring the lateral loads to the columns and floors/foundations. It is recommended for a diaphragm to be tied into the structure, such as the walls, as this achieves box like behaviour which is beneficial as the structure will move relative to the ground and not vibrate out of phase. Modelling Assumptions When modelling in “RESIST” a number of assumptions were made to simplify the building for ease and consistency of modelling to meet the programs limitations. Assumptions where based of what RESIST can and cannot take into account and consist of the following:-) No account taken for openings and there effect on the structure A Simplified rectangular floor plan will be used Medium Soil Wind Region W As the building is a heritage building it was placed in importance category 3. The Floor Live Load was office as a hotel at full capacity is similar to the high loads from large groups of people seen in offices. Floor weight is to be heavy after retrofits added at 100mm concrete slab with added tiles Roof weight to be light as it is of timber construction with corrugated iron. Exterior Wall weight is heavy due to the 200mm block concrete walls and masonry block walls. Interior Wall weight is to be medium as it is a combination of both timber and concrete and masonry walls. X-Direction to run North to South in Orientation Y-Direction to run East to West in Orientation. Majority of materiality in a direction will be the chosen lateral structure. Original Structure to have Concrete Masonry Walls in the X-Direction extending the whole length of the wall Original Structure to have Concrete Wall in the Y-Direction extending the whole length of the wall Walls to be added internally in the Y-Direction as Concrete Masonry in the Southern end of the building Brick Masonry Walls to be 10% of the actual length Reinforced concrete walls to be 40% of the actual length Initial Results Although the results from Resist show the building is at 46% of the NBS standard in the X-Direction and its ultimate limit state which makes it an EQ prone building, as a building should be at the minimum standard of 100%, it can be said that the model was under-predicted. This is as a number of elements were unable to be accounted for such as openings or the parallelogram like shape of the structure which would all effect and change the results by increase their percentage of failure. Recommended Action Option 1 After assessing the performance of the building it is recommended that 4.5m 200mm thick sprayed concrete skin is to be applied over steel reinforcing on the internal Eastern side of the building to decrease the effects of torsion from a lateral load applied (Leuchars. 1989). This is recommended as it is a system with comparable stiffness to the original masonry meaning that the vibrations experienced in a seismic event will be in phase and lead to less damage being incurred as elements wont “smash” into one and other when vibrating compared to what they may act like in the 1st and 3rd nodes of frequency (Leuchars. 1989). Option 2 Eccentrically braced frames with stiffeners to prevent localized buckling will be fixed to the concrete walls in both the Y and X direction in the North Eastern and South Western corner of the building. This will increase the rigidity in that direction due to an EBF (Eccentrically braced Frame) being a triangulated structure. When designing for an EQ you design for the deformation, an EBF allows for large deformations at the yield point without incurring much more load which ensures movement relative to the ground and less damage to the building due to being ductile. Application will occur either on the external façade or internal façade depending on client preference but in both instances it will be tied into the walls and extend vertically both storeys (Thomas. 2017). Conclusion In conclusion it was decided to use an EBF to reduce the effects that in plane loads have on the masonry walls after achieve a “box like structure”. By using an EBF the centre of rigidity of the structure will improve by moving to the same location as the centre of mass and hence reduce the potential for torsion to occur as all shear forces will be distributed laterally. Other improvements which could be made, although they cannot not be modelled in Resist consist of the following; 1) An edge beam shall to be added to take the compression and tension forces present in the diaphragm regardless of the beams not taking any gravity loads. 2) It is also recommended that as the building has a service/baggage lift shaft and is within close proximity to other buildings an earthquake belt should be added to separate structures as they will possibly resonate at different frequencies and cause an increase in damage. 3) As mentioned previously there are 3 voids through the roof diaphragm. It could be recommended that one stair set is removed and trim beams added to reduce the overall flexure of the roof diaphragm however this will hinge on whether or not the building will still meet code in terms of access and Evac routes with fire safety. 4) Finally to avoid a potential stress concertation all walls shall be retrofitted so there is no disconuitiy of wall thickness. This is as a tensile stress could be generated where a change in direction is located with the second floor concrete framed wall meets the ground floor timber framed wall. References Leuchars, J.M. The use of Sprayed Concrete in The Strengthening of earthquake Risk Buildings. Bulletin of the New Zealand National Society for Earthquake Engineering. Volume 22. No 3. September 1989. < http://www.nzsee.org.nz/db/Bulletin/Archive/-.pdf > Miranda, B. Torsional Considerations in Building Seismic Design. NZSEE Conference. 2012 < https://www.nzsee.org.nz/db/2012/Paper055.pdf > Scarry, J.M. Floor diaphragms – Sesmic bulwark or Achilles heel. NZSEE Conference. 2014 < http://db.nzsee.org.nz/2014/oral/19_Scarry.pdf > Thomas, Geoff. Seismic Design 2. 16/08/2017. Te Aro: Lecture Theatres VSLT2. Lecture Thomas, Geoff. Seismic Design 4. 16/08/2017. Te Aro: Lecture Theatres VSLT2. Lecture Appendices Initial Results/Report Option 1 Results/Report Option 2 Results/Report Council Plans Figure 6 Section AA Section BB Reinforced Concrete Block Timber Framing Concrete Floors Ceddar Diaphragm Corrugated Iron Masonry Brick Wall Concrete Foundations Axonometric Schematic Depicting the Structural Systems of the Building Collums and Beams Walls and Diaphragms N Key 100mm Concrete Slab with Reinforced Mesh Reinforced Concrete Block Walls Concrete Collumns Brick Masonry Wall Brick/Timber/Concrete Block Partitions Concrete Tie Beams Ceddar Roof Diaphragm Parapets Tied to Bond Beam Figure 5 Work Submitted for Assessment Declaration Form Student’s full name : Samuel John Leith Pendreigh Course : BILD 322 Assignment/project (number and title) : Assignment 2 Date submitted : 09/28/2017 _____________________________________________________________________ Refer to the information on Academic Integrity, Plagiarism and Copyright on the back of this form. 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