Comparisons of Tensile Structure with Conventional Steel Structure

: Tensile structures represent a new chapter in the history of building structures. Non-linear material behaviour, large strains and displacements and the use of fabric action to resist loads require a fundamentally different approach to structural analysis and design compared to steel structures. The analysis consists of temporary rectangular shed for steel structure and tensile structure, to carry out the form finding and load analysis of each structure and report key values of stress, deflection and reactions. The results show very high levels of variability in terms of stresses, displacements, reactions and material design strengths, and high light the need for future work to harmonise analysis methods and provide validation and benchmarking for fabric analysis software .The procedure is incorporated into the RFEM Software and the results of some analyses are given.


I. INTRODUCTION
A tensile structure is a construction of elements carrying only tension and no compression or bending.Tensile structures are the most common type of thin-shell structures.A tensile membrane structure is most often used as a roof, as they can economically and attractively span large distances.Most tensile structures are supported by some form of compression or bending elements, such as masts, compression rings or beams.steel structure is a metal structure which is made of structural steel components connected to each other to carry loads and provide rigidity.Because of the high strength of steel, these structures are require more raw material than some other types of structure such as tensile structure.They can maintain high ratio of applied load to self -weight, as compared to steel and concrete structure for same span.Fabric structures possess several advantages over conventional steel structures.Perhaps most importantly, fabric can span large distances without incurring much weight on supporting structure or foundation.They are capable of carrying large applied loads while weighing very little in comparison to steel or concrete structures of the same spans.This reduction in weight and material translates into shorter construction schedules and overall cost savings.

II. SHAPE AND FORMS OF TENSILE STRUCTURE
These shapes were discovered by Otto and Berger during their investigation of natural forms such as soap bubbles.There are two types of general shapes: anticlastic and synclastic shapes.Anticlastic shapes are created by having the radii of the principal curvatures on opposite sides of the tension fabric surface.Some examples of anticlastic shapes are saddle, cone, etc. synclastic shapes are characterized by having the radii of the principal curvatures on the same side of the fabric like a dome.

Dead Weight
The dead weight is assumed including all the fittings.Absorption of liquid is not possible, so any addition in the dead load due to water ingress is not possible.

Imposed Loads
Referring to the table 2 Clause 4.1 of IS875 (Part 2) With slope greater than 10 degree imposed load is calculated as given below Angle of the line joining top and bottom end is 11.3 degree.Therefore, 0.75 -0.02 x (11.3-10) = 0.724 KN/m^2 .Minimum live load 0.4 kN/m^2 for tensile structure.Internal Pressure Coefficients Cpi The internal pressure coefficients Cpi can be determined from 7.3.2 of IS 875-3:2015.For this structure, it is assumed the total opening on the wall is less than 5 to 7 percent of the total wall area.Therefore, the Cpi values for this example are +0.5and-0.5.

External Pressure Coefficients Cpe
The External Pressure Coefficients Cpe depend on certain parameters such as height, width, length, roof angle, and roof profile.For this structure, since the roof profile is gable or duopitch, the roof external pressure coefficients will be calculated based on Table 6 of IS 875-3:2015.For this example since h/w = 0.3, and the roof angle is 11.3°, the Cpe values will be interpolated using the following values.
For wind angle = 0 degrees:

Roof angle
Zone EF -Windward Zone GH -Leeward 10° -0.9 -0.4 V. RESULT The Design of Steel structure and tensile structure was completed using RFEM Software and the results are tabulated from the Analysis Report.Design of both the Structures was optimized for all the governing factors.The Design of both structures was used to derive the steel out-take, economic liability and material specification.It was concluded through statistical and graphical analysis that the tensile canopy outclassed the conventional steel space frame on the parameters such as steel required and cost effectiveness.Results show very high levels of variability in terms of stresses, displacements, reactions and material design strengths.For most output parameters there is a wide spread of values.It is difficult to generalise but the standard deviation and the interquartile range are both commonly 25-50% of the mean value.2. Tensile structure allow for higher energy savings, a consideration that is becoming ever more important to the green building industry.3. Tensile structure structures employing polyester or other material subject to creep strain under prestress, retensioning may be carried out in conjunction with inspection 6 to 12 months after completion and for steel structure not need to prestress.4. Wind loads are the main consideration for membrane structures and steel structure.

Figure 1
Figure 1 Forms of tensile structure

Figure 3 Figure 4
Figure 3 Global deformation of Tensile structure structure (Lakh) Cost of structure (Lakh)