3.3 Material Selection
3.3.1 The steels adopted for the structure for mobile communication engineering steel tower and mast shall be characterized by qualified tensile strength，elongation，yield strength，sulfur content and phosphorus content.The welding structure shall have qualified carbon content.
The steels adopted for welding structure and important non-welding bearing structure shall pass the cold bend test.
3.3.2 Q235 carbon structural steel，Q345 low alloy structural steel and 20# high-quality carbon structural steel shall be preferred for adoption for the structure for mobile communication engineering steel tower and mast.Q390 steel or structural steel with higher strength grade，when necessary，may also be adopted.The quality standard shall comply with GB/T 700 Carbon Structural Steel，GB/T 1591 Low-alloy High Strength Structural Steel and GB/T 699 Technical Conditions for High-quality Carbon Structural Steel respectively.
Grade A Q235 carbon structural steel shall not be used for the member to be welded；Q235 rimmed steel shall not be adopted if the operating temperature of main compression member is equal to or less than-20°C in winter.
3.3.3 The galvanized steel wire rope and steel strand are preferred for the guy of guyed steel mast.The quality standard shall comply with GB/T 8918-1996 Steel Wire Rope and YB/T 5004-2001 Galvanized Stranded Wire respectively.
3.3.4 The jointing materials shall meet the following requirements：
1 The manual arc welding should be adopted for the structure for steel tower and mast.The electrodes selected shall comply with the current national standards，namely GB 5117 Carbon Steel Covered Electrode or GB 5118 Low Alloy Steel Electrode.The electrode model shall be matched with the strength of member steels，and may be selected based on the following principles：
1）E43XX electrode should be selected for Q235 steel；
2）E50XX electrode should be selected for Q345 steel；
3）E55XX electrode should be selected for Q390 steel；
4）The electrode which is matched with low strength steels may be selected for attachment weld of steels with different strength.
2 The welding wire and corresponding welding flux shall be matched with base metal strength when applying automatic welding or semi-automatic welding.To weld steels with different strengths，welding materials may be selected according to the steel with lower strength.The welding wire and flux shall comply with GB 1300 Welding Wire and Flux for Fusion Welding.
3 The plain bolts may be selected to connect the angle steel tower which shall comply with GB 5782 Hexagon Bolt-Grade A and B and GB 5780 Hexagon Bolt-Grade C.
4 The high-strength plain bolts should be selected to connect the steel tube with flange，and highstrength bolt may be made of 45# steel，40Cr，40B or 20MnTiB steel and shall comply with GB/T 1228～GB/T 1231 Technical Conditions of Large Hexagon Head Bolt，Hexagon Bolt and Washer for Steel Structure.
5 The anchor bolt should be made of Q235，Q345 steel，35# or 45# high-quality carbon steel without welding.
3.3.5 The design of material frequently used for the structure for steel tower and mast shall meet the requirements set out in the following table:
Table 3.3.5-1 Design strength value of steel/N·（mm2）-1
Notes：①The thickness in above table refers to the thickness of steels at the calculation point.In terms of axial tension and compression members，it refers to the thickness of thicker plate in the section.
②The design strength value of 20#high-quality phosphorus steel（seamless steel tube）is the same as that of Q235 steel.
Table 3.3.5-2 Design value of connection strength of bolt and anchor bolt/N·（mm2）-1
Notes:①Grade A bolt is used for d≤24mm，l≤10 d or l≤150mm（whichever is less）；Grade B bolt is used for d＞24mm，l＞10 d or l＞150mm（whichever is less）.d is nominal diameter，and l is nominal length of screw.
②The accuracy and the roughness of hole wall surface of Grades A and B bolt holes and the allowable deviation and the roughness of hole wall surface of Grade C bolt hole shall comply with Check and Acceptance Specifications of Structure for Mobile Communication Engineering Steel Tower and Mast.
Table 3.3.5-3 Design value of weld strength/N·（mm2）-1
Table 3.3.5-3（continued）
Notes:①The mechanical property of deposited metal for welding wire and flux adopted for automatic welding and semi-automatic welding shall not be less than the provisions of current national standards GB/T 5293 Carbon Steel Wire and Flux for Submerged Arc Welding and GB/T 12470 Fluxes for Submerged Arc Welding of Low Alloy Steel.
②The weld quality grade shall comply with GB 50205 Code for Acceptance of Construction Quality of Steel Structures.For butt weld with thickness of less than 8mm，the ultrasonic flaw detection shall not be adopted to determine the weld quality grade.
③The design value of bending strength of butt weld in compression and tension zones are
and 
respectively.
④The thickness in above table refers to the thickness of steels at the calculation point，and the thicknesses of axial tension and compression members refer to the thickness of thicker plate in the section.
⑤The design value of weld strength of 20#high-quality carbon steel is the same as that of Q235 steel.
Table 3.3.5-4 Design value of strength of galvanized stranded wire for guy/N·（mm2）-1
Table 3.3.5-5 Design value of strength of steel wire rope for guy/N·（mm2）-1
3.3.6 The design value shall be multiplied by corresponding reduction coefficient to calculate the following structural member or connection：
1 Single sided single angle steel：
1）The strength and connection is calculated based on axis stress：0.85；
2）The stability is calculated based on axis stress.
Equal angle steel：0.6+0.0015λ，but not more than 1.0；
Unequal angle steel with short side connected：0.5+0.0025λ，but not more than 1.0；
Unequal angle steel with long side connected：0.7.
Note：λ is slenderness ratio.The discrete compression rod of single angle steel in the middle shall be calculated based on the minimum radius of gyration.But，when λ＜20，λ=20 is taken.
2 High-altitude erection weld with poor construction conditions：0.90.
Note：if the two situations exist at the same time，the reduction coefficient shall multiply repeatedly.