Steel Structure: Cutty Sark, MaryRose Museum and Titanic Museum - Case Study Example

Steel structures literature Steel structure: Cutty Sark, MaryRose museum and Titanic museum Steel structures remain pivotal to design of major structures across the globe. Today, more than ever, steel structural design has emerged as a fundamental engineering design discipline and a pillar to modern structural advancement. Additionally, with the rising number of extreme occurrences, safety awareness alongside the technological advances in building design innovation suggests the importance of steel and growth of structure. Steel structures design are guided by codes and standards which offer benchmark design considerations. Over the years, the structural industry has transitioned from prescriptive design to performance-based design, which has consequently increased the need for structural performance testing and analysis. A combination of technological advances, increased research, and need for prediction of structural behavior. Nonetheless, understanding past designs offers immense potential for understanding design challenges, failures, and hence come up with more effective designs. Understanding design specifications require a comprehensive analysis of structural steel plates, shapes, bars, as well as rivets used in construction of structures. These are important elements which shape strength of structures. This section reviews steel structural design with specific emphasis on three legendary structures; Cutty Sark, MaryRose museum and Titanic museum MaryRose Museum The museum’s steel structure has rounded ends designed to resemble a ship’s hull, and more specifically, Mary Rose’s hull while the roof was installed on prefabricated units and supported by 32m long rafters. It has two conventionally piled pavilions on its either sides. The lead structural designer, Warings paid special attention to the frame to ensure its effectively fit Mary Rose. The biggest challenge in the frame’s design was in erection of the main beams over Mary Rose ship. However, this was overcome by splitting the beams into 3 sections with 2 fixed to side columns initially, while the central section was the last to be positioned. The lifting of the central section was aided by a 20% oversized mobile crane and a sling supporting the beam at each of the ends. Additionally, cherry pickers were used in bolting the central section to the main section with the cherry picker baskets encapsulated with netting and tools tethered using lanyards to lower falling objects risks. Metsec steel framing was attached to the frame as well as black stained timber reminiscent of the ship’s hull. In order to create way for new steel structure, the Weymss structure’s width had to be reduced. Additionally, a temporary, insulated curtain was set to maintain temperatures around Mary Rose ship. The design also incorporated new columns to support roof beams of the Weymss structure. They were erected close to Mary Rose, loads transferred and sections of Weymss structure roof beams currently extending beyond new columns, cut off. Further, steel frame elements passing through the Weymss structure were later sealed up. It is important to note the initial design by Ramboll, also a structural engineer involved a steel bridge over the protected dry dock, and supported by 4, 1.5m piles. However, this was re-designed by Warings from heavy steel structure, supported by four piled support points outside line of existing dock, to a lightweight framing solution, with partially bearing within the dock. This design immensely lowered risks and also reduced the construction budget to sustainable levels. The structures’ main steel columns sit on pads isolated from dock’s stonework through a structural membrane. The pads further help in even distribution of the structure’s load. From the dock, the steel framing rises up, enclosing the hull within the elliptic shaped structure. As mentioned, the frame includes two pavilions, on northern and southern structure’s side, with one housing the entrance foyer and the other accommodates the educational suite. Additionally, the building’s irregular shape was formed using several faceted columns. Cutty Sark The Cutty Sark is an epitome of great age of sail and the last surviving tea clipper. Its preservation was therefore a milestone achievement in historic preservation. The design/conservation solution raises Cutty Sark 3m high within constraints of dry berth, allowing for new interventions that respects the ship’s original fabric. The sophisticated and elegant pre-stressed system hangs the ship and also stabilizes its new position (Crevello & Noyce, 2008). Additionally, the steel frame is expected to preserve the ship’s hull shape, in addition to enabling creation of a public space in the beneath dry berth and hence allow visitors to walk below and admire its form. The project incorporates innovative use of structural steel. Design of the project’s steel structure involved digital modeling of its detail prior to construction. Costing was also done throughout the process to allow for design optimization and management. The Cutty Sark’s steel enclosure incorporated 12 steel frames connected through a longitudinal beam measuring 500 by 40mm at the top. This is below the tween deck and has its bottom grounded to the newly designed keel plate that is fastened to existing keel on the entire ship (Stoyanov, Mason & Bailey 2010, pg. 650). The frames are made from horizontal compression members cambered, with internal diagonal tie rods fastened to the keel plate. The plates had been hidden under the ship’s planking when they had been welded. When restoration was completed, the new skeleton had to be hoisted on to supports. These were composed of steel compression struts that are hollow, with a capacity of 50 tons. They were coupled to node points found at the end of each of the cradle frames where they stuck out through the hull. The external support’s lower ends were linked to plates cast into the dry dock’s steps. Since the steps had started crumbling, they had to be dug out and reinforced with grouted steel piles before connecting supports and lifting the ship. A series of arms offered lateral wind load restraint. The arms were bolted to strengthened concrete tension piles at the top of the dry dock (Douglas 2012, pg. 69). The connection nodes are also required as secondary support to the glass canopy. The members’ structural steel grades are of S355 J2 to BS EN 10025. The ship’s weight redistribution involved lifted at regular intervals along its length to allow installation of 12 new triangulated steel frames. The frame took the form of an inverted coat hanger, with two tie rods from ship’s keel running diagonally up to each end of a horizontal strut spanning the width of the ship beneath the Tween Deck (Gregory, 2008). This inverted hanger frame carries the weight of the ship’s keel and masts back up to the new external support points. The 12 sets of horizontal beams and diagonal ties form a triangle between the strake plates and new box keelson which encases the ship’s original keel, fixing its vertical position and preserving the ship’s iconic shape from within. There is an extra cradle that completes the system connecting the ship’s stern to the keel. Further, the new steel cradle is integrated with existing fabric of ship wherever possible. Additionally, the cradle system is fully adjustable using giant turnbuckles set in the primary ties and struts, ensuring a perfect fit to existing ship fabric and dry berth. The 24 inclined struts carry the ship’s weight. Titanic Museum, Belfast The structure rises off a transfer slab and includes 4 concrete-reinforced steel hulls, replicating Titanic ship. The sloping facades, stability as well as ease of construction were major construction in adopting this steel structure. The concrete cores are flexibly designed to allow advancement ahead of floors as is the case on traditional steel structures. The design is such that construction was undertaken hull by hull (Littlefield & Jones, 2013). The eastern side of the atria consists of a row of vertical column frames while on the western side; the vertical load is distributed in four mega columns, each of varying trapezoidal profiles fabricated using 25mm thick steel plates reinforced with concrete. The columns extend from the lowest level to the underside level. Further, the floor beams are designed in form of composite cellular beams using a 150mm deep concrete slab on profiled steel metal decking. This is further accorded optimal flexibility to allow service integration. The design further endeavored to ensure that the fifth floor’s Banquet Hall be column free. A 30m clear span girder was used to achieve this. Conclusion The evaluated steel designs offer valuable lessons for future consideration of steel structure design and construction. Both negative and positive issues emerge. Firstly, phase by phase construction of steel structures largely features. Conventional, when construction of steel structure is done in phases, an opportunity is availed for review of the completed phases prior to commencement of the next phase and as such limit losses which may be incurred due to unforeseen errors in the initial phases of a project. The issue of flexibility also prominently features in all the three projects considered. As a matter of fact, non-flexible techniques such as welding are only used where no better alternatives exist. This allows ease of repair works if need be and is in line with Eurocode 3 which requires that steel structure be as flexible as possible. Repairs can therefore be done on the affected components rather than the entire structure if need be. In the case of Cutty Sark, digital modeling is used highlighting the importance of modeling such structures and even more, simulating their operational environments prior to implantation. Another important aspect emerging in review of these designs is flexibility which prominently features Eurocode 3 guidelines as well as other international steel structure construction guidelines. Further, the cases reveal that salts, sulfates and chlorides are harmful to the conditions and durability of steel enclosures. Where they exist, sulfate-resistant materials (concrete, steel) will have to be used as defined in Standard Specification Item 421 and other relevant regulations for construction in soils with high sulfate content or seawater. Designers and contractors must consult the list of recommended corrosion protection (Eurocode 3) for specific areas that may have structures with possible corrosion due to sulfate soil or salt water (Beedle, Ali & Armstrong 2007, pp. 18). The use of steel in corrosive environments is often not recommended. If it must be used a suitable coating must be selected, more section provided or a combination of these techniques applied to ensure proper performance of materials. Additionally, they described highlight an area where steel structure design is guided by function/location rather than aesthetic considerations. As a matter of fact, this is an area where aesthetics has been relegated to lower levels of consideration. Factors such as, design load magnitude, dictates the required size and shape of the enclosure from a structural perspective. Economic considerations also largely feature in steel structure design and involve comparison of costs and materials. The structure further dictates mode of construction and the appropriate materials. References Beedle, L. S. Ali, M. M., & Armstrong, P. J. (2007). The skyscraper and the city: design, technology, and innovation. Lewiston: Edwin Mellen Press. Crevello, G. & Noyce, P., (2008). Conserving the Cutty Sark. Journal of architectural conservation, 14(2), 49-67. Douglas, L. (2012). The Cutty Sark is back. Engineering & Technology, 7(9), 68-71. Gregory, R. (2008). Key contemporary buildings: plans, sections, and elevations. New York: W.W. Norton. Littlefield, D. & Jones, W. (2013). Great modern structures: 100 years of engineering genius. Carlton, London. Stoyanov, S., Mason, P., & Bailey, C. 2010, Smeared shell modeling approach for structural analysis of heritage composite structures – An application to the Cutty Sark conservation. Computers & Structures, 88(11-12), 649-663. Read More