Load calculation and profile selection for combined supports and hangers
The load calculation and profile selection for combined supports and hangers are the basis for ensuring the safety and reliability of the supports. Load calculation is divided into permanent load and live load: Permanent load (G) — includes the self-weight of pipelines of each discipline, the weight of the medium inside the pipes (water pipes calculated as full of water, air ducts do not consider medium weight), insulation layer weight, and cable weight (calculated at 40% cable tray fill rate). Calculation formula: G = G pipeline 1 + G pipeline 2 + ... + G pipeline n. Reference values for typical pipeline self-weight: DN100 fire pipe (including pipe weight + full water) approximately 22 kg/m, DN150 fire pipe approximately 38 kg/m, 1000*250 air duct approximately 18 kg/m, 300*150 cable tray (including cables) approximately 15 kg/m. Live load (Q) — installation and maintenance load: concentrated load considered as 500 kg (assuming 1-2 installers working on the support), uniform live load considered as 1.0 kN/m2. Seismic load (E) — in accordance with GB 50011-2010 Code for Seismic Design of Buildings, horizontal seismic forces shall be considered in areas with seismic fortification intensity of 8 or above. Load combination: for ultimate limit state design, the load partial factors are taken as 1.2 (permanent load) + 1.4 (live load) or 1.35 (permanent load) + 1.0 (live load), whichever is greater. Profile selection: Cross beams (members subjected to bending moment) use hot-rolled channel steel (8#, 10#, 12# channel steel, material Q235B) or C-shaped steel (41*41, 41*52, 41*62, material Q235B hot-dip galvanized). Bending moment calculation formula M=G*L^2/8 (simply supported beam with uniform load) or M=Q*L/4 (concentrated load at mid-span), bending stress sigma=M/W, allowable bending stress [sigma]=215 MPa (Q235B). Columns (members subjected to compression-bending) use hot-rolled channel steel or equal-leg angle steel (L50*5-L80*8), and the compression-bending stress check is performed according to the axial compression formula (considering slenderness ratio and stability coefficient). Suspension rods use hot-dip galvanized fully threaded rods (diameter 10 mm, 12 mm, 16 mm), and the tensile capacity is calculated according to the formula N=A*[sigma] (e.g., the effective cross-sectional area of an M10 suspension rod is approximately 58 mm2, tensile capacity 58*215=12470 N=1.27 t), with a safety factor of not less than 1.5.
Layout strategy and application of combined supports and hangers
The layout strategy of combined supports and hangers directly affects the stability and economy of pipeline installation. Layout principles: Determination of longitudinal spacing — the longitudinal spacing of combined supports and hangers shall not exceed the maximum spacing of supports and hangers for the most stringent pipeline among the carried pipelines (e.g., the maximum spacing of supports and hangers for DN100 water pipes is 6.0 m, the maximum spacing for DN150 water pipes is 7.5 m, the suspension rod spacing for air ducts with long side below 800 mm is 3.0 m, and the cable tray spacing is 2.0 m), usually controlled by the minimum spacing of 2.0 m, and in actual projects 3.0 m is often adopted (balancing economy and safety). Location selection — combined supports and hangers should preferably be arranged near structural beams (not more than 500 mm from the structural beam), so that loads are directly transferred to the structural beams (floor slab has greater bearing capacity), avoiding arrangement at the mid-span of the floor slab (floor slab has lower bearing capacity). In corridor areas, combined supports and hangers should be uniformly arranged along the longitudinal direction of the corridor (spacing 3.0 m), and the starting end shall not be more than 1.5 m from the corridor end. Coordination with single-discipline supports — for heavier pipelines (such as pipes above DN200, large air ducts, etc.), single-discipline reinforced supports should be added between combined supports and hangers (spacing reduced to 1.5-2.0 m) to distribute loads. For light pipelines (such as weak current cable trays, fire signal cable trays, communication cable trays, etc.), they can be directly fixed on the combined supports and hangers (no separate supports are required). Pipeline fixing method — on the cross beam of the combined supports and hangers, each pipeline should be fixed with dedicated pipe clamps or hangers (water pipes with U-shaped pipe clamps, air ducts with angle steel brackets + flat steel straps, cable trays with channel steel brackets + bolts), and rubber liners should be provided between the pipe clamps and pipes (for vibration isolation and corrosion protection). The arrangement of pipelines on the cross beam should be left-right symmetrical (to prevent eccentric load causing torsion of the cross beam), with heavy pipelines arranged in the center (e.g., the main fire pipe DN150 placed in the center of the cross beam) and light pipelines arranged on the sides (e.g., weak current cable trays placed on both sides of the cross beam). Installation precautions — during the installation of combined supports and hangers, the suspension rods should be fixed first (drill holes in the floor slab and install expansion bolts or chemical anchors), then the cross beam should be installed (adjust the levelness deviation to not exceed 3 mm/m), and finally each pipeline should be installed. Pipeline installation sequence: install air ducts first (the largest and non-bendable), then water pipes (heavier), and finally cable trays and conduits (lighter and more flexible).
Anti-corrosion and fireproofing treatment of comprehensive supports and hangers
Anti-corrosion and fireproofing treatment of comprehensive supports and hangers are necessary measures to ensure the service life of the supports and fire safety. Anti-corrosion treatment: Environmental classification — according to GB 50046-2018 Standard for Anticorrosion Design of Industrial Buildings, indoor dry areas (guest rooms, corridors, offices, etc.) are mildly corrosive environments, indoor humid areas (bathrooms, kitchens, pump rooms, laundry rooms, etc.) are moderately corrosive environments, and outdoor areas (roofs, outdoor corridors, etc.) are severely corrosive environments. Selection of anti-corrosion measures — Indoor dry areas: hot-dip galvanizing (average galvanized layer thickness not less than 65 um, conforming to GB/T 13912-2020), or 2 coats of anti-rust paint (epoxy zinc-rich primer + epoxy topcoat, each coat with dry film thickness not less than 40 um). Indoor humid areas: hot-dip galvanizing (average galvanized layer thickness not less than 85 um) + epoxy topcoat (dry film thickness not less than 50 um), or supports and hangers made of stainless steel (304 stainless steel). Outdoor areas: hot-dip galvanizing (average galvanized layer thickness not less than 85 um) + polyurethane topcoat (dry film thickness not less than 80 um), or stainless steel (316L stainless steel). Galvanized layer repair — operations such as cutting, welding, and drilling during the installation of supports and hangers will damage the hot-dip galvanized layer; zinc-rich primer (zinc content not less than 92%, dry film thickness not less than 50 um) should be applied immediately to the damaged parts, and the coating should cover 20 mm beyond the damaged area. Fireproofing treatment: according to GB 50222-2017 Code for Fire Protection Design of Building Interior Decoration, comprehensive supports and hangers require fireproofing treatment in the following areas: supports and hangers crossing fire compartments (such as inside pipe shafts and on both sides of fire walls), supports and hangers installed in evacuation corridors (requiring fireproof coating), and supports and hangers in high-temperature areas (smoke exhaust machine rooms, boiler rooms). Selection of fireproof coatings — fireproof coatings for steel structures: ultra-thin type (thickness 2–3 mm, fire resistance rating 1.0–2.0 h, used in indoor visible areas, good decorative effect), thin type (thickness 3–7 mm, fire resistance rating 1.0–2.5 h), thick type (thickness 8–30 mm, fire resistance rating 1.5–3.0 h, used in concealed areas). Application method: ultra-thin and thin fireproof coatings may be applied by spraying or brushing (each coat with dry film thickness not exceeding 0.5 mm, applied in multiple coats to the design thickness), and curing for not less than 48 h after application.
Support and hanger load verification and acceptance standards
After the installation of combined supports and hangers is completed, load verification tests must be carried out to ensure that the load-bearing capacity of the supports meets the design requirements. Load verification method: Loading method — use staged loading. First, select the heaviest pipeline among all pipelines installed on the support crossbeam and apply load to it (usually the main fire protection pipe or air-conditioning duct), and apply load in stages at 50%, 75%, 100%, and 125% of the design load (using sandbags or water bags for loading, with each stage lasting 15 min to observe deformation). Deformation measurement — install a dial indicator or laser distance meter (accuracy 0.01 mm) at the midspan of the support crossbeam to measure the deformation under each load stage (elastic deformation and residual deformation). Acceptance criteria — the maximum deformation shall not exceed L/200 (L is the support span). For example, when the span is 1.8 m, the maximum deformation shall not exceed 9 mm, and after unloading, the residual deformation shall not exceed 1 mm (i.e., permanent deformation less than 1 mm). Load-bearing capacity verification — when loaded to 1.25 times the design load, each component of the support (crossbeam, column, suspension rod, connecting bolt, anchor bolt, etc.) shall not show obvious deformation, slippage, loosening, or fracture. Acceptance inspection items — support installation position (consistent with design drawings, deviation ±20 mm), installation elevation (deviation ±5 mm), levelness (deviation ±3 mm/m), verticality (deviation ±3 mm/m), welding quality (welds full and free of cracks, undercut depth not greater than 0.5 mm), bolt tightening (torque values according to design values, M12 bolt tightening torque 40-60 N*m), anti-corrosion coating (no missed coating, no rust, no peeling), fireproof coating (thickness meets design requirements, no missed coating, no cracking). Acceptance records — all acceptance data shall be recorded in the "Combined Support and Hanger Installation Acceptance Record Form" (including drawing number, support number, load test data, deformation data, inspection items, inspector signature, acceptance date), and kept on file.