Portal frame buildings and design concepts 4
Types of Portal Frames 4
Truss Frame Buildings Design Concepts 5
Types of Trusses 6
Cladding Types for Steel Buildings 7
Types of Cladding 7
Portal Frame buildings construction 9
Shallow foundation design and construction 10
Types of Shallow Foundations 10
Deep foundation design and construction 12
In the world of engineering, to build even the most complex structures, steel structures are utilized to implement qualities like art, beauty and functional capability together through structures in innumerable ways due to the sustainability, cheap cost, and flexibility of design, reusability and its adaptability in developing steel structures. Steel allows freedom to combine with other materials to fuse and originate as an aspiring structure. Structural design in the aspect of engineering can be recognized as an amalgamation of science and art. Steel is considered one of the most significant building materials since the renaissance era. (Buildings Department, Hong Kong, 2011) The common usage of steel in buildings can be due to the advantages observed in its utilization. It became a household name in engineering scenarios as it was fully recyclable in many ways reducing the overall cost of a structure. This amount of overall usage of steel throughout the world caused the origin of various new concepts and technologies to be developed specifically for structural steel designs and construction methods related specifically to construction of steel buildings. (Adluri, n.d.) The evidence that steel construction has very strongly stood the test of time is that even today, the world’s tallest buildings and longest bridges are constructed with the help of steel. Steel structures became commonplace at such a global level as the construction utilizing steel materials wasn’t hindered by any weather conditions and it became available in abundance throughout the world. The construction design concepts surrounding the usage of steel in structural construction designs have been developed and have been under usage and study for a long time.
Portal frame buildings and design concepts
Steel Portal frames are utilized commonly for low-rise structures consisting dominantly of horizontal or pitched rafters and columns all joined by moment resisting connections. It has been derived that they are efficient if used for low rise structures or single storey buildings given that the design is cost-effective and there is a productive choice of design parameters and assumptions. It is abundantly used for pitched roof buildings due to its economically versatile range of spans. Portal frames are found to be structurally efficient with functional form. There many types of portal frames widely used along with many different variants under use.
Types of Portal Frames
1) Tied Portal Frame: In this type of portal frame, the spread of the eaves and the bending movements are largely decreased. There is a development of large compression forces in the rafters which leads to reduction of stability among the members.
2) Mono Pitch Portal Frame: As a reason for close proximity to other to other buildings, mono pitch frames are used for their small spans. It is a simplified for of the pitched roof frame and is commonly used for comparatively smaller buildings.
3) Pitched Roof Frame: It is mainly framed from UKB sections with a limited span of measurement for various dimensions with a large eaves haunch section fabricated from plate. It is one of the most commonly used types of portal frame.
4) Crane Portal with Frame Brackets: There is a possibility of brackets being fixed to the columns for supporting the crane rails in case a travelling crane is required which is of relatively low capacity.
5) Portal Frame with Mezzanine Floor: When there is a requirement of an office structure within the frame, there is a partial block created with mezzanine floor.
6) Propped portal Frame: When in a situation, the requirement of a clear span is absent and the span of the portal frame is substantial, a propped frame can be put under usage to minimize the span of the rafter and also horizontal shear at the foundations.
Truss Frame Buildings Design Concepts
Trusses are mainly a triangulated system of linear interconnected structural elements. The individual elements inside the trusses are adjoined by nodes while it is often referred also as open web girder. They are widely utilized in a broad range of buildings which possess a requirement for very long spans often noticed in airports and auditoriums or they are used to carry heavy loads by implementing trusses in transfer structures. Similar to Portal Frames, Trusses are also utilized for single story buildings and structures. Trusses serve two primary functions which are carrying the extensive roof load and providing superior horizontal stability in a structure. The two types of arrangements noted among trusses of which one is an arrangement providing lateral stability using portal trusses and other one is the arrangement using vertical trusses supported by columns. (Rinke & Kotnik, 2010)
Types of Trusses
1) Pratt Truss: This type of truss is also familiar through the name of ‘N’ Truss. In a conventionally recognized Pratt Truss, gravity loads are provided diagonal members in case of tension and are generally used where there is predominance in gravity loads.
2) Warren Truss: Warren Trusses are often put to use in long span buildings ranging in length 20 to 100 meters. It is notable that this type of truss utilizes lesser members than a Pratt truss. When there is maximized restraint on to the internal members, larger spans of warren truss may be adapted.
3) North Light Truss: In case there is necessity for trusses in a short span building which can be a workshop or a similar type of space, North Light Trusses are used for gaining a benefit from the natural lighting available in a structure.
4) Saw-tooth Trusses: It is a different version of the North Light Truss while being similar to it, the change noticed here is a distinct vertically perpendicular structure. It is primarily utilized in multi-bay buildings. (Jayachandran, 2009)
Cladding Types for Steel Buildings
Cladding initially began when there was a necessity of bonding a metal coating into another metal for installing an insulating structure outside a building; metals undergo cladding under high amounts of heat and pressure. There are 3 primary forms of cladding undertaken when used for steel buildings:
Types of Cladding
1) Profiled Sheeting: It is recognized as one of the most common methods of cladding under use since many years. Also known as corrugated sheeting, it is a form of cheap cladding available for industrial buildings which is extensively used in many buildings. Usually steel or aluminum is used for profiled sheeting. It is designed for superior toughness and resistance to external heat.
2) Cassette Panels: Panels generally tend to be formed with rectangular shapes and edges on the sides. The usage of the term cassette with panels indicates usage of several types of panels starting from simple sheets folded from panels. Cassette panels originated through the French engineer Jean Prouve. They are formed usually by brake pressing or folding flat metal sheets. (Tata Steel, n.d.)
3) Composite panels: Composite panels as such are known for their structure which consists of two steel sheets that are bonded in a sandwich-like construction on the sides of foam’s insulating core or material similar to it. This panel essentially provides better stiffness, in addition to which surfaces – smooth and profiled are present. These panels are placed by methods such as self-drilling, secret fixing brackets and self-tapping screws that are present inside the joints of the panel. (n.a., n.d.)
Portal Frame buildings construction
Advantages of Portal Frame Construction
• Erection is more easy and speedy
• Buildings can be made watertight.
• Until the time that the framework is ready, drainage and road construction (site works) can be carried out.
• Framework erection is unaffected by the weather.
(Sansom & Miejer, 2002)
Disadvantages of Portal Frame Construction
• Steel bends easily when hot, irrespective of its incombustible properties.
• Corrosion- prone
Portal Frame structure has 3 types of connection systems:
• Rigid base
• 2 pin
• 3 pin
These types are classified on the basis of the rigidity and flexibility of the connection which are related to the parts such as the base, knee and the apex. Furthermore, it also can be related to a large extent with the structure’s load transfer, owing to the bending issue. The rigid based connection systems are used more often in the construction today owing to its characteristic ability to give the framework a far lighter finish because of the bending moment correction and axial load lifting. Pinned bases on the other hand, transmit the bending moment straight through to the foundation.
Shallow foundation design and construction
Foundations are a critical part of construction and concerning the efforts and resources required for it, shallow foundations prove more feasible and economical than shallow foundations considering the case that there is not a necessity for foundations to be established deep within the ground. There are certain situations required for executing a shallow foundation. (Civil Engineering and Development Department , 2006) The first requirement would be a suitable amount of soil bearing capacity for a shallow foundation for safety concerns. The other requirement for shallow foundation is undisturbed soil or engineering fill.
Types of Shallow Foundations
Spread footings: Any building’s foundation is made up of a base to which “spread footing” is a structural component. These structures are made by concrete and additional support is provided by the reinforcement of steel. These footings can be buried way below the usual ground level or a few feet below it, depending on the requirement. (U. S. Department of Transportation, 2010)
Combined footings: This type of footing is provided under the following circumstances:
• When columns are very near to each other and their individual footings overlap.
• When bearing capacity of the soil is less, requiring more area under individual footing.
Mat or raft foundation: Mat or Raft foundation can be useful when it comes to soil that has a low bearing capacity or at places where the columnar structure and other similar areas are very near to each other in both the directions, causing the individual pads to almost touch each other. The utility of the raft foundation can be classified as spreading the load in an area widely, and providing rigidity to the structure, in turn strengthening the weaker areas in the soil.
(Alhassan & Boiko, 2013)
Deep foundation design and construction
The foundations which register the depths of the foundations in a greater number as compared to its width are recognized are deep foundations. They can also be recognized by their construction methods which do not come under the open pit excavations. They are used in cases where the strata of the good bearing capacity are unavailable near the ground and the space is restricted to contain spread footing. (Alhassan & Boiko, 2013)
Most common forms of construction pertaining to deep foundations are:
• Pile Foundation (more commonly used in building construction)
• Caisson or Well Foundation
Pile Foundation: The term ‘Pile Foundation’ denotes a construction for the foundation of a wall or pier which is supported on piles. It is mostly used where steep slopes are encountered or compressed/waterlogged soil is found on site. (Patra, Das, & Shin, 2005)
Cofferdams: Cofferdams are usually defined as
“ a temporary structure constructed in a river or a lake or any other water bearing surface for excluding water form a given site to enable the building operation to be performed on dry surface.” (Patra, Das, & Shin, 2005)
Caissons: Generally made of wood, reinforced concrete or steel, Caissons are erected by connecting it with the excavation and are used as foundation for bridges, abutments in river and dock structures in lakes for the protection of shores. (Patra, Das, & Shin, 2005)
Adluri, D. S. (n.d.). Structural Steel Design. Canada: Memorial University.
Alhassan, M., & Boiko, I. L. (2013). Experimental Study of the Effect of Foundation Shape on Settlement and bearing Capacity on Soils. International Journal of Engineering and Technology , 108-114.
Buildings Department, Hong Kong. (2011). Code of Practice for the Structural use of steel. Hong Kong: Buildings Department.
Civil Engineering and Development Department . (2006). Foundation Design And Construction. Hong Kong: The Government of the Hong Kong .
Jayachandran, P. (2009). Preliminary Design and Optimization. National Workshop on High-rise and Tall Buildings (pp. 1-20). Hyderabad: University of Hyderabad.
n.a. (n.d.). Composite Panels. Retrieved 10 2014, 7, from www.huntsman.com: http://www.huntsman.com/polyurethanes/a/Products/Construction/Asia%20Pacific/Applications/Composite%20panels
Patra, C. R., Das, B. M., & Shin, E. C. (2005). ULTIMATE BEARING CAPACITY OF ECCENTRICALLY LOADED STRIP FOUNDATION ON SAND REINFORCED WITH GEOGRIDS. DSpace (pp. 335- 344). Bangkok: Dspace.
Rinke, M., & Kotnik, T. (2010). The changing concept of truss design caused by the influence of Science. London: Taylor & Francis Group.
Sansom, M., & Miejer, J. (2002). Life-cycle assessment (LCA) for steel construction. European Commision.
Tata Steel. (n.d.). Cassette panels. Retrieved 10 2014, 7, from www.tatasteelconstruction.com: http://www.tatasteelconstruction.com/en/reference/teaching_resources/architectural_studio_reference/cladding/metal_cladding/cassette_panels/
U. S. Department of Transportation. (2010). SELECTION OF SPREAD FOOTINGS ON SOILS TO SUPPORT HIGHWAY BRIDGE STRUCTURES. U. S. Department of Transportation.