RULES / ENGINEERING
New conveyor on existing steel: what to check first
The loads a new conveyor puts on an existing steel structure — dead, live, belt tension, dynamic, impact, blocked-chute surcharge, wind — and the nine checks to make before the equipment is ordered.
Part of the guide: How to specify a bulk material conveying system
The most common late surprise on a conveyor project is not the conveyor. It is the steel the conveyor was going to sit on: a gallery drawn for a lighter belt, a transfer tower that lost a bracing member to a past modification, a roof that was never meant to carry a head pulley. The check itself is not expensive. It becomes expensive when it is done after the equipment has been ordered.
Why does existing steel catch projects out?
Because a conveyor looks light. The equipment is often a modest load; the material on it, the tension in the belt and the things that happen when it starts, stops or blocks are not. A structure that has stood for decades under one set of loads gives no visible warning that a new set will be different, and the old drawings, where they exist, describe a building that has since been altered, corroded and loaded in ways nobody recorded.
Which loads does a conveyor bring?
The load list a supplier provides should cover all of these. The third column is where the surprises usually come from.
| Load | Where it acts | What usually gets forgotten |
|---|---|---|
| Dead load | Stringers, idlers, pulleys, drive, covers and walkways, along the whole run | Covers and walkways added after the first estimate |
| Material live load | The carrying strand, at the design rate | A belt loaded to the surcharge line after a stop, at wet density |
| Belt tension | Head, drive, tail and take-up pulleys, as a horizontal pull | It rises when the belt is retensioned, and the take-up mass hangs somewhere |
| Start-up and dynamic loads | Drive frame and head pulley supports | Starting torque well above running torque on a direct-on-line start |
| Impact | Chute supports and the loading zone | Drop height and lump size; impact idlers pass the blow to the stringers |
| Blocked-chute surcharge | Transfer chutes and hoppers | A chute packed solid to the top is a column of material the steel has to hold |
| Wind and weather | Covers, gallery cladding, handrails | New covers add sail area to a frame that never had any |
| Maintenance loads | Walkways, lifting beams, pulley-change points | Two people, a pulley and a chain block on a beam nobody sized for them |
What are the rules?
Find the original drawings and calculations
Steel drawings, foundation drawings, the calculation note if one exists, and every modification drawing since. They say what the structure was designed to carry and where its margins were meant to be. If they cannot be found, the survey has to do their work and the assumptions have to be conservative.
Survey the steel as it is, not as it was drawn
Walk it with a torch and a tape. Look for corrosion and section loss at column bases and under leaking chutes, holes cut for pipes and cables, bracing removed for access and never replaced, connections with missing bolts, and loads the drawings never showed — a hoist, a dust filter, a bridge to the next building.
List every load, not just the weight
The equipment weight is the easy part. Add the material at the design rate and on a full stopped belt, the belt tension as a horizontal force at each pulley, the start-up torque at the drive, impact under the chutes, a blocked chute, wind on covers, and the people and tools of a pulley change. The table above is the checklist.
Follow the load path to the foundations
A new support on a beam loads the beam, then its connections, then the column, then the base plate and the foundation. A member that passes on its own can still overload the one below it. Check each link down to the ground, and ask what the foundation was cast on.
Check the connections, not just the members
Bolted and welded connections are where old structures usually fail a check. A beam with ample capacity in bending can hang from a cleat sized for a fraction of the new reaction, and a horizontal belt tension puts forces on connections that were only ever designed for vertical load.
Respect vibration and fatigue
Drives, elevators, screens and out-of-balance pulleys load steel millions of times a year. Members adequate for the static load can crack at welds and bolt holes under cyclic load, and a light frame can be excited at its natural frequency by a motor. Stiffness and damping matter here, not strength alone.
Never hang anything from purlins or cladding rails
Purlins carry the roof and cladding rails carry the wall; neither is designed for a point load, and both are usually thin cold-formed sections. Supports go to primary members — beams, columns, trusses — or to new steel that carries the load to them. The same applies to grating, handrails and pipe supports.
Agree responsibilities before the order
The conveyor supplier provides the support reactions and the load list. The owner of the structure has it checked by a structural engineer, who says whether the steel passes, what strengthening it needs, or whether the loads must go elsewhere. Write down who does which part, and by when, so the check is not left to whoever notices first.
Get it signed off before anything is ordered
The structural check, with any strengthening it calls for, is a condition of placing the equipment order, not a task to run alongside fabrication. A conveyor that arrives before its supports are proven waits on site, and the strengthening then happens in the shutdown window that was meant for installation.
What if the steel does not pass?
There are options short of walking away: strengthening members and connections, adding a support so that the loads land on a column rather than a beam, moving the drive or the take-up to steel that can carry them, choosing a lighter arrangement, or building a new structure alongside the old one. Which of these makes sense is part of the retrofit or replace decision, and a feasibility study is where the structure is checked early enough for the answer to change the design rather than delay it.
On paper, the support points and their reactions belong on the general arrangement and the load list that accompanies it. The specification guide sets out where the structural check sits in the sequence, and our design and engineering work produces the load list the structural engineer needs to begin.
QUESTIONS WE HEAR
Can the conveyor supplier check the existing steel?
The supplier's job is to give the loads: support reactions, belt tensions, dynamic factors and the weight of everything in the scope. Checking the steel is structural engineering on a structure the supplier neither owns nor designed, so it is normally done by the plant's structural engineer or one the plant appoints, unless that work is explicitly written into the scope.
What if there are no drawings of the building?
The survey replaces them. Section sizes are measured, connections photographed and sketched, and the steel grade is either assumed conservatively from the age of the building or established by testing a sample. The result is a set of as-built drawings good enough for the check. It takes time, which is a reason to start early.
Does a small screw conveyor need a structural check?
Yes. A screw trough is usually supported from a floor or hung from above, and a trough full of material — as it will be when the discharge blocks — weighs much more than the empty conveyor on the drawing. The hangers, the beam they attach to and the floor plate all need to be looked at.
How much does a conveyor weigh?
It depends on width, length, the material carried and what is on it — covers, walkways, drives — so no useful single figure exists. The supplier's load list gives the dead weight, the material load and the pulley forces at each support. Ask for it with the proposal, because it is the input the structural check cannot start without.