Qualification - Higher National Diploma in Construction
Unit Name - Principles of Structural Design
Unit Number - Unit 20
Unit Level - Level 4
Unit Code - R/615/1406
Unit Credit - 15
Assignment Title - Warehouse Building structural design
Learning Outcome 1: Calculate bending moments and shear forces for simply supported steel and concrete beams.
Learning Outcome 2: Determine deflection for simply supported steel beams.
Learning Outcome 3: Calculate the axial load carrying capacity of steel and reinforced concrete columns.
Learning Outcome 4: Explore design methods for steel, reinforced concrete beams and columns.
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Assignment Brief
Scenario Context
You work for an SME (Small or Medium Enterprise) size organisation of a Design and Construct Structural Engineers, Fifth Column Ltd as an intermediate Structural Design Engineer. Your role is to assist your senior colleagues in all aspects of the job. You are learning both on the job and with part time study at college towards your qualifications to eventually become a Chartered Engineer. Before you worked in the design office you worked on site for a year with a mentor to see and understand some of the practical aspects of the job.
1. ABSTRACT:
Fifth Column Ltd. has recently won a project for the design and construction of a warehouse building. The warehouse spans in longer and shorter direction are 35.53m and 26.192m, respectively. As an assistant to senior design engineer, preliminary design solution of warehouse is assigned. The architectural plan of warehouse is given. The standard planning loads are applied upon the warehouse slab. The loads increment factors -as per BS standards- 40% and 60% for dead and live loads are applied upon slab. The effective net design load on slab is 21.30KN/m2. After calculations of load path in two-way slab system, the load distribution on longer span (35.53m) and shorter span (26.192m) comes out to be 228.67KN/m and 185.96KN/m respectively (Britannica, n.d.). The steel beams are designed using BS-5950under applied loading conditions, the beam sections in longer and shorter span comes out to be UB 533 x 210 x 122 and UB 533 x 210 x 109 respectively. The load from beams would ultimately be transferred upon the designed column 254 x 254 x 63. In the end, SFD, BMD and maximum deflection on beam A along grid line A is calculated under uniform load of 10KN/m and point load of 40KN is calculated and analyzed. The overall objective of this project is achieved, and this final report will be submitted in design office and will be reviewed by seniors. If the senior's committee found this design satisfactory, the report will be forwarded to client(FIONA, 2008).
Task 1: There are a few months before the project starts on site while planning permission is obtained, the senior engineers are all very busy with existing projects. You have been tasked therefore to prepare a report on the feasibility of the various structural options which might be used for the project.
An Executive Summary and an introduction to the project and your appointment.
Solution:
INTRODUCTION:
I, Eng. ...............have been appointed as Assistant design engineer for project 16883 "Design of Warehouse". Our firm- Fifth Column Ltd - have won a project for the design and construction of a warehouse building. The warehouse building plan is given by the architect. Hence, we need to design the warehouse meeting all architectural, financial, site, environment, and sustainability constraints. The clear span of warehouse is 35.53m in E-W and 26.192m in N-S direction, covering total area of 930m2. The walls are 100mm block (inner face),100 mm cavity with 75mm of insulation, and 100mm of reconstituted stone facing up to 4m high, with 1500mm wide piers up to roof height. And profiled steel cladding between at4m to 8m, the height of the building walls. Height to the building roof apex is9.5m (civildigital, n.d.).
I have been appointed to prepare a feasibility of various structural options that might be used in warehouse construction, meeting all possible constraints. Hence, using my engineering knowledge and on field experience, different structural options would be evaluated, and the best suited option would be recommended to senior. The senior engineer would evaluate the report and pass on the final remarks on design report. The final decision would rest with senior engineer and client (HULSE et al., 2000).
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Analyse the various different support methods and the materials used for beams and columns in fixed structures in general and their effect on deflection in fixed structures. Include their load carrying capacity, size, weight and corrosion resistance properties.
Solution:
SUPPORT METHODS AND MATERIALS FOR STEEL AND RCC STRUCTURES:
In fixed structures, different types of support or end conditions may exist in field. The structural supports provide stability and stiffness to resist internal stresses caused by applied loads, and safely transfer them to the foundation. The supports can be classified as end supports or intermediate supports. In our case of warehouse design-Owing to architectural constraints- we aren't allowed to provide any intermediate support. A roller support is ideal for providing the lateral movements in structure e.g., Thermal expansion. But it can resist load only in perpendicular plane, any lateral load would cause roll away of structure. The Pin support is usually termed as shear connection as it attached the web of beam to the girder. Fix supports hold the two members in fix position (istructe, n.d.).
For beams, Fix-Fix, Fix-Pin, and Roller-Pin end conditions prevails in construction. These supports are main load transferring agents. The load from slab is directly applied upon beams. The applied load is resisted by beams and transferred to column through end supports. The load path is the main key in determining the flow path of loads. Each end condition has its own pros and cons (Britannica, n.d.).
The deflections in structure may be classified as local -member- deflection and structural deflection. The deflection in rigid structures is reported in terms of the angular movement and the vertical displacement. The simply supported beams offers much resistance to deflections than cantilever. The cantilever support is resisting the load from one end;therefore, the free end is more susceptible to deflect (SEWARD, 2003).
Universally, Concrete and steel are the two chief materials being used in structures. The beams and columns may be of either concrete or of steel. The steel beams and columns are preferable in structures having longer span e.g. In our case, Warehouse. These are available in different shapes. The strength of steel structure is satisfactorily accepted worldwide. But iron oxide paints and corrosion resistance coatings are effective in resistance against corrosion.The steel structures are slightly costlier than concrete one's, it's because of high material price and skilled labor is required to complete the project (civildigital, n.d.).
Explain the statutory requirements for the structure in general , using current codes of Practice, approved documents and building regulations to ensure safety in structural designs, including the valid factors of safety for live loads, dead loads and imposed loads, and how maximum bending moments could determine steel beam selection In terms of economics and safety.
Solution:
STATUTORY REQUIREMENTS AND LOAD:
Statutory requirements ensure safety and economy in design of structures. The statutory requirements are standardized in the form of construction and design manuals. These standards make sure the application of design parameters. The main statutory requirements may include compliance of engineering structure with structure, energy, sustainability, and local building codes. While in engineering terms, the Statutory requirements may be load carrying capacity of structure, serviceability limits, bearing capacity of foundation and the individual capacities of members of structures (iabse, n.d.). The key in design and Statutory requirement is that the structure must have ability to resist the applied loading under existing conditions within acceptable range of resource. To ensure safety of design, the applied loads and moments are factored up using standard load factors. As per BS recommendation, the dead and live loads are increased 40% and 60% respectively to accommodate any increases and accidental loading. The factor of safety is solely depending upon engineer's perception and the existing site conditions (FIONA, 2008).
EFFECT OF MAX. BENDING MOMENT ON STEEL BEAM DESIGN:
The increased moments demanddeep cross sections of steel. It is because θM = θ Fy*Zx. Hence, the maximum moment bending moment is directly proportional to the depth of cross section of steel beam. Therefore, for higher moments, deeper structural steel cross sections are required to resist the applied loadings and moments. And deeper cross-sectional elements increase overall cost of project (Britannica, n.d.).
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Evaluate and explain about the use of the various alternative materials which might be used in achieving a design solution for the warehouse building, discussing the benefits or challenges associated with each material type. Include within your evaluation the implications of the axial load carrying capacity of steel columns and reinforced concrete columns, how deflection in beams affects structural stability and describe the concepts of slenderness ratio and how this might impact on the warehouse project.
Solution:
COMPARISON B/W STEEL AND RCC DESIGN ALTERNATIVES FOR WAREHOUSE DESIGN
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PROPERTY
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CONCRETE
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STEEL
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Labor
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No need for skilled labors
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Needed skilled labor.
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Modes of failure in column
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Compression failure, slender failure, tension failure
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Squashing capacity, Flexural buckling capacity, Torsional buckling capacity, Local buckling capacity.
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Load carrying capacity of Columns
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ΦPn = Φc*Fcr*Ag
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For tied columns,
Pu = ΦPn = 0.8Φ [0.85fc′(Ag - Ast) + Astfy]
For spiral columns,
Pu = ΦPn = 0.85Φ [0.85fc′(Ag - Ast) + Astfy]
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Load carrying capacity of Beams
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(Md)= Phi*As*fy(d-0.5a)
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Φ M= Φ F*S
F= Maximum allowable stress
S= Plastic Modulus
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EFFECT OF SLENDERNESS RATIO ON COLUMN DESIGN:
The slenderness ratio is the ratio of the column height, L, to the radius of gyration. The effect of slenderness could be neglected, and the column could be designed as a short columnwhen,
KLu/r < 34 -12M1/M2 < 40
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Once you have explained and presented the alternative structural solutions and implications of these for the project assess the most effective support method for the warehouse building in terms of ease and speed of construction, economics, safety and environmental factors.
Solution:
PROS AND CONS OF STEEL STRUCTURE
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Lightness
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Susceptibility to corrosion
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High strength per unit weight
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High initial cost
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Can easily be fabricated
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Skilled labor
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Fast installation at site
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No sudden failure
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9. PROS AND CONS OF CONCRETE STRUCTURE
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Composite material e.g., Raw material easily available
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efflorescence due to presence of salts
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Flexibility in fabrication for different shapes
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High Self weight of concrete
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High Compressive strength
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weak in tension
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Prestressing
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creep in structures.
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Impermeable e.g.,Watertight structures
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Drying shrinkage and Cracking
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Develop and present a preliminary design solution, including the beam design and column design, and produce outline sketch drawings and a scope of works specifications in support of the structural design solution you have proposed.
Write a summary and a conclusion for the report based on your findings, analysis and evaluations.
Solution:
DESIGN OF WAREHOUSE:
The construction of warehouse in given span conditions would be best suited using steel structure. The architectural configuration is showing the column configuration. The total load from structure will be transferred from roof slab to structural joists and these joists would transfer the load to beams. The load from beams would be transferred to columns and ultimately, will be transferred on the foundation. The steel structure is suitable because of its low weight to strength ratio, easy fabrication and erection, and suitability for structures like Warehouses, storages etc (istructe, n.d.).
The longer and shorter span of warehouse is 35.53m and 26.192m respectively. The standard dead and live loads upon warehouse are considered. The dead load includes as 75mm thick concrete slab laid over 20GA metal deck. The dead load of slab and metal deck is 1.125KN/m2 and 0.12KN/m2 respectively (Britannica, n.d.). For roofing and resistance against environmental effects, three ply ready roofing with bituminous smooth surface waterproofing membrane is considered. The dead load of roofing comes out to be 0.05KN/m2 and 0.07KN/m2 respectively. In warehouse, for ceiling suspended ducts and ceiling light fixtures, the effect of above ceiling suspended dead load is taken as 0.1KN/m2. The live load on warehouse with heavy storage is taken as 11.97 KN/m2. The dead and live loads are factored using BS factors e.g., 40% increase in dead load and 60% increase in live load (iabse, n.d.).The ultimate effective load on warehouse slab comes out to be 21.30 KN/m2.
As we know that load from slab is transferred on beams in two methods. One way slab method and two-way slab method. In our warehouse case, the ratio of longer to shorter span is less than two (2). Hence, two-way load travel path will be analyzed. The load in two-way slab is transferred to beam through uniform trapezoidal and uniformly varying load distribution (SEWARD, 2003). Hence, the uniform load of 21.30 KN/m2 is transferred on beam B1 and B2, the resultant load comes out to be 228.67KN/m and 185.96KN/m, respectively. The beams are designed using BS 5950Blue steel manual. The UB beams under applied loading -after proper design- comes out to be UB 533 x 210 x 122 and UB 533 x 210 x 109. The load from beams would be transferred to columns. The column design is also carried out using BS 5950Blue Steel Manual. Under applied loading, the C254 x 254 x 63 section of column is best suited to resist applied loading. The manual handwritten calculations and the structural plan of warehouse is attached below (FIONA, 2008).