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Space Truss DesignEngineering Postgraduate Program Hasanuddin University 15 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 2005SPACE TRUSS DESIGN1. DESIGN SPECIFICATION1.1. Design Standard1) The design basis of the tower applied is EIA Standard EIA-222-E Structural Standards for SteelAntenna Tower and Antenna Supporting Structure. The fabrication and materials of the tower willbe according to the relevant Indonesian Standard.2) The self supporting tower has square cross sections.3) All the legs and bracings are made of equals legs angles steel.4) All the connections in the field are made with Steel Bolts, each fitted with one spring washer andnut.1.2. Tower Structure Design Condition1) Tower height : 42.0 meter ( location : Limboto, North Sulawesi )2) Maximum wind velocity (V) : V = 120 km/hour = 33.33 m/sec.3) Existing antennas loading ( see the drawing attachment ) :- 2 (two) Planar type antennas at 42.0 m- 1 (one) Planar type antennas at 38.0 m- 1 (one) Paraboloid grid antennas 1.20diameter at 35.0 m- 1 (one) Paraboloid grid antennas 1.20 diameter at 42.0 m4) Proposed antennas loading ( see the drawing attachment ) :- 1 (one) Paraboloid solid antenna 1.2 diameter at 38.0 m1.3. Loads1) Dead loadDead load is weight of tower, antenna, ladder, platform etc.2) Wind load on tower structureWind load calculation method on the tower and appurtenances are as followsF = qz . GH . CF . AE and not to exceed2 . qz . GH. AGqz = 0.613 . KZ . V2Kz = ( z / 10 )2/7GH = 0.65 + 0.60 / ( h / 10 )1/7CF = 4.0 e2 5.9 e + 4.0 ( square cross section )CF = 3.4 e2 4.7 e + 3.4 ( triangular cross section )e = AF / AGAE = DF . AFWhere :F = Horizontal wind force ( N )qz = Velocity pressure ( Pa )GH = Gust response factor ( 1.00 s Kz s 1.25 )CF = Structure force coefficientAE = Effective projected area of structural component in one face ( m2)AG = Gross area of one tower face ( m2)Kz = Exposure coefficient ( 1.00 s Kz s 2.58 )V = Basic wind speed for the structure location ( m/s )Space Truss DesignEngineering Postgraduate Program Hasanuddin University 16 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 2005z = Height above average ground level to midpoint of the section ( m )h = Ttotal height of structure ( m )e = Solidity ratioAF = Projected area of flat structural component in one face of the section(m2)DF = Wind direction factor1.00 for square cross section and normal wind direction1.00 + 0.75e for square cross section and 450wind direction3) Wind load on AntennaWind load calculation method on the parabolic antenna is as follow :Fa = Ca x A x Kz x GH x V2Fs = Cs x A x Kz x GH x V2Kz = ( z /10 )2/7GH = 0.65 + 0.60 / (h/10)1/7Where :Fa = Axial Force (lb)Fs = Side Force (lb)Ca = Wind load coefficient for axialCs = Wind load coefficient for sideKz = Exposure coefficient ( 1.00 s Kz s 2.58 )z = Height above average ground level to midpoint of the section(m)h = Total height of the structure (m)A= Normal projectedarea of AntennaV= Wind velocity ( m/s )4) Load combinationHerewith the following combinations are used below :a) DL + WLat 0 degree direction (with weight of existing antenna)b) DL + WLat 45 degree direction (with weight of existing antenna)c) DL + WL at 0 degree direction (with weight of existing + proposed antenna)d) DL + WL at 45 degree direction (with weight of existing + proposed antenna)Where : DL = Dead load weight of the structure and appurtenances.WL = Design wind load on antenna at above direction.1.4. Allowable unit stressTheunitstressesinthestructuresmembersdonotexceedtheallowableunitstressesforthematerialsasspecified in the AISC Standard (American Institute of Steel Construction Standard)1. Tension : Ft = 0.60 Fy ( kg/cm2)2. Shear : Fv = 0.40 Fy ( kg/cm2)3. Compressioni) On the gross section of axially loaded compression members when kl/r is less than Cc :(kl/r)2[ 1 - ----------] Fy2Cc2Fa = ----------------------------------------------- ( kg/cm2)5/3+ [3/8(kl/r)]/8Cc - [(kl/r)3/8Cc3]Space Truss DesignEngineering Postgraduate Program Hasanuddin University 17 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 20052t2EWhere: Cc = ---------Fyii) On the gross section of axially loaded compression members, when kl/r exceeds Cc :12t2EFa =--------------- ( kg/cm2)23(kl/r)24. BendingTension and compression on extreme fibers : Fb = 0.66 Fy ( kg/cm2)5. Tension on bolts : Ft = 0.60 Fy ( kg/cm2)6. Shear on bolts : Ft = 0.30 Fy ( kg/cm2)7. Bearing on bolts : Ft = 1.20 Fu ( kg/cm2)8. The maximum slenderness ratio (kl/r) are as follows :kl/r = 120 for compression members of legskl/r = 150 for compression members of diagonalskl/r = 200 for tension membersNotations :Ft = Allowable tensile stress ( kg /cm2)Fy = Minimum yield point ( kg /cm2)Fv = Allowable shear stress ( kg /cm2)Fa = Allowable compressive stress ( kg /cm2)k = Effective length factorl = Actual unbraced length of member ( cm )r = Governing radius of gyration ( cm )Cc = Column slenderness ratioE = Modulus of elascity of steel = 2,100,000 kg/cm2Fb = Allowable bending stress ( kg /cm2)Fu = Minimum tensile strength ( kg /cm2)1.5. MaterialsSteel materials to be used for the towers and appurtenances conform to the relevant Indonesian Standardsand/or Japanese Industrial Standard.1) Steel StructuralDescription Tensile Strength( kg/cm2 )Minimum Yield Point Fy( kg/cm2 )Bj 41 4100 2500SS 41 4100 25002) BoltsDescription Ft Fv FvSpace Truss DesignEngineering Postgraduate Program Hasanuddin University 18 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 2005Friction Type Bearing Type( kg/cm2 ) ( kg/cm2 ) ( kg/cm2 )A 325 Bolts 3900 1230 14763) ConcreteDesign compressive strength of concrete (fc) at 28 days.K - 175 - fc = 175 kg/cm24) Reinforcement steelU - 24 - Fy = 2400 kg/cm21.6. Structural AnalysisThe purpose of the structural analysis is to find the joint translations and the design axial loads in all membersof the tower. Load is applied and separate load cases combined to give the most severe design conditions atvarious section.The structural calculation is made using SAP 90 (Structural Analysis Program 90). The program will performthe static analysis of a space truss of arbitrary geometry by the stiffness method. The truss may be subjectedto loads consisting of forces acting on the joints in any directions in space. The program output consists of thejoint translations, the member forces and the support reactions.The program input contains :a. Structure titleb. Loading system : number of static analysis that applied to the structure.c. Group of data correspondingto the properties of the mathematical model of truss and the applied jointload :- Group 1 : Joint coordinates- Group 2 : Support joint restraints- Group 3 : Material and member data- Group 4 : Joint loads- Group 5 : Loading combinationsThe location of the joints in any structure are expressed as coordinates in a global right hand othogonal XYZcoordinate system. For the space structures the Z axis is oriented in the vertical direction positive upward,with the X and Y axes oriented in the major directions of the structure.Global AxisAll applied joint loads, joint displacement and reactions are expressed as component in the global coordinatesystem. Force component and translation components are positive if they act in the positive direction of anaxis.The member forces and support reactions for both conditions, tower with existing antennas and tower withexisting and proposed antennas, are attached in computer output.1.7. Design Calculation Of FoundationThe calculation of foundation consists of design and control of foundation.Control of foundation includes :Z +X +Y +0Space Truss DesignEngineering Postgraduate Program Hasanuddin University 19 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 20051) Control of stability for uplift force :Sf = W1 / T > 2.0Where : W1= Weight of foundation and soil ( kg )T = Uplift force ( kg )2.0 = Allowable safety factor2) Control of bearing capacity of soil :Wt MF = -------- +--------------- 1.5Where : SF = Safety factorWt = Total vertical loadincludes support reaction, weight of foundationandweight of soil (kg)| = Coefficient of soil frictionH = Horisontal loads ( kg )1.5 = Allowable safety factor2. STRUCTURAL CALCULATIONThe structural analysis is made using SAP 90. Input and output program is shown as attachment.Deflection, sway and twist are calculated as follows :a. Deflection : Dxn : Joint displacement at a point nDxn : Joint displacement at a point nDxn Dxnb. Sway angle = arc tan ( --------------------------------------------------------- )Distance between point n and point nDxn Dxnc. Twist angle = arc tan ( ---------------------------------------------------------- )Distance between point n and point n1) Tower without proposed antennaa. Deflection = 6.4177 cmb. Dxn = 5.2096 cmSpace Truss DesignEngineering Postgraduate Program Hasanuddin University 20 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 2005Dxn = 5.8865 cmd = 250 cmSway angle = arc tan (( 5.8865 5.2096 ) / 250 ) = 0.1551 degreec. Dxn =5.8865 cmDxn = 6.4173 cmd = 300 cmTwist angle = arc tan (( 6.4173 5.8865 ) / 300 ) = 0.1014 degree2) Tower with proposed antennaa. Deflection = 6.5947 cmb. Dxn = 5.2534 cmDxn = 5.9388 cmd = 250 cmSway angle = arc tan (( 5.9388 5.2534 ) / 250 ) = 0.1570 degreec. Dxn = 6.4763 cmDxn = 5.9388 cmd = 300 cmTwist angle = arc tan (( 6.4763 5.9388 ) / 300 ) = 0.1027 degreeSway and twist at 120 km/hour wind velocity without proposed antennas as follows :Actual AllowableDeflection (cm) 6.4177 42Sway angle (degree) 0.1551 0.5Twist angle (degree) 0.1014 0.5Sway and twist at 120 km/hour wind velocity with proposed antennas as follows :Actual AllowableDeflection (cm) 6.5947 42Sway angle (degree) 0.1570 0.5Twist angle (degree) 0.1027 0.5Space Truss DesignEngineering Postgraduate Program Hasanuddin University 21 B. OF DUCTILE STEEL STRUCTURES. Yoppy Soleman, 20053. FOUNDATION ANALYSIS3.1. Column Anchorage Bolt Calculation1 1) Steel Bar Bj 37 --------- Fy = 2400 kg / cm22 2 ) Notation :Fy = Yield strength of s