Structural Fasteners
Fasteners for steel frames, bridges, cladding systems and precast connections, in grade 8.8 and 10.9 steel with hot dip galvanizing and zinc flake coatings. Preload and slip critical behaviour specified with the joint, not after it.
Structural Fastener Applications
A structural joint is designed around the connection, not around the bolt. Whether the connection is bearing type or slip critical changes the specification completely, and getting it wrong is a design error rather a procurement one. These six assemblies are where that distinction matters.
Steel Structures and Building Frames
Whether the joint is bearing type or slip critical. A slip critical joint cannot be coated on the faying surface at all.
Grade and coating selected with the connection type in mind, and thread fit confirmed where hot dip galvanizing is used.
Typical parts Hex bolts, structural nuts, hardened washers, HSFG assemblies
Bridges and Pedestrian Structures
Fatigue under cyclic traffic loading, plus a corrosion allowance over the design life with no maintenance access.
Coating system matched to the exposure, and material certificates that support the design life calculation.
Typical parts Structural bolts, shear connectors, bearing and expansion joint hardware
Cladding and Facade Systems
Visible fasteners that must not stain the facade, and brackets that carry wind load into the structure.
Stainless and coated systems selected so staining does not migrate onto the surrounding surface.
Typical parts Facade fasteners, bracket bolts, self drilling screws, rivet nuts
Roof and Wall Systems
Self drilling into thin sheet without distorting the thread, and a coating that survives being drilled.
Self drilling geometry matched to the sheet gauge, with coatings that retain protection at the drilled edge.
Typical parts Self drilling screws, stitching screws, insulation fasteners, roof bolts
Formwork and Falsework
Repeated assembly and stripping cycles, so the fastener is reused many times and must not strip the thread.
Thread form and grade chosen for reuse, with hard washers that do not brinell under preload.
Typical parts Wing nuts, tie rod components, clamp bolts, reusable thread bar
Precast Concrete Connections
Cast in hardware that has to be located accurately before the pour and stay aligned afterwards.
Machined cast in parts with locating features, supplied with dimensional reports for the setting out.
Typical parts Cast in sockets, anchor channels, lifting anchors, connection plates
Why Structural Buyers Work with GUXIANG
We manufacture rather than trade, so forming, threading, heat treatment and finishing sit inside one facility. On a structural part that matters because the coating thickness, the thread fit and the material certificate all have to agree with each other, and a handover between suppliers is where that agreement usually breaks.
Connection type respected
Bearing type and slip critical joints are specified differently, and the difference is a design decision rather than a purchasing preference. We ask which one you have before quoting.
Slip critical and bearing joints quoted separately
Thread fit with HDG
Hot dip galvanizing adds zinc to both threads, so the tap is sized for the coating rather than for the bare thread. Confirmed before production, not at assembly.
Oversize tapping or masking agreed in advance
Preload method matched
Turn of nut, calibrated wrench and direct tension indicator washers each suit different joints. We supply the hardware that matches the method your specification calls for.
DTI washers and calibrated hardware available
Weathering systems selected by site
Coating systems are selected against the corrosivity category of the actual site rather than against a generic outdoor specification.
ISO 12944 category used to select the system
Not sure whether your joint is bearing type or slip critical?
Send the connection detail or the drawing reference. We will identify the connection type, confirm whether the faying surface can be coated, and flag the thread fit if hot dip galvanizing is specified.
Property Classes and Preload Control
A structural bolted joint is controlled by preload, not by bolt strength. Two methods are used in practice, and which one applies changes both the hardware and the inspection regime.
| Method | How preload is achieved | Verification | 注 |
|---|---|---|---|
| Snug tightened | Nut run down to contact the plies | Visual, plus specified rotation | Bearing type joints only, no designed preload |
| Turn of nut | Snug, then a specified further rotation | Rotation angle recorded | Simple, needs consistent snug tightness |
| Calibrated wrench | Torque applied with a calibrated tool | Torque value recorded | Friction dependent, wide scatter on coated threads |
| Direct tension indicator | Washer deforms at target load | Gap measured with a feeler gauge | Most reliable on site, independent of friction |
| Tensioning device | Hydraulic stretching of the bolt | Load displayed on the device | Large diameters, high accuracy |
Preload method should follow the connection design and the project specification rather than availability on site. A calibrated wrench gives poor repeatability on coated threads because friction varies between batches and between positions, which is why direct tension indicator washers are often specified where the preload is critical.
Coatings for Structural and Outdoor Service
Structural coatings are selected by the corrosivity category of the site and by whether the joint is slip critical. The same coating that protects a bearing joint can destroy a slip critical one.
| 系统 | Corrosion class | Faying surface | Thread fit affected | 典型用途 |
|---|---|---|---|---|
| 热浸镀锌 | 非常高,非常高,非常高 | Must be masked if slip critical | Yes, tap oversize | Coastal structural, long life |
| Zinc flake, non electro | 非常高,非常高,非常高 | Can be specified to a slip class | 极简 | Bridges, slip critical joints |
| Dacromet / Geomet | 非常高,非常高,非常高 | Can be specified to a slip class | 极简 | Offshore and coastal steelwork |
| Zinc nickel | 高 | Not for slip critical | 极简 | Facade and cladding hardware |
| Zinc aluminium mechanically plated | 高 | Can be specified to a slip class | 极简 | Structural fasteners |
| Stainless, uncoated | Stainless base | 不适用 | 不适用 | Facade and architectural |
A slip critical connection cannot be coated on the faying surface. Slip resistance depends on a defined coefficient of friction between the connected plies, and any coating on that surface changes the coefficient and can eliminate the slip capacity the connection was designed for. Coatings are applied to the bolt, the nut and the washer, and the faying surface is left clean and uncoated unless the design explicitly specifies a friction class coating. If a slip critical joint is galvanized over the whole assembly, the connection has to be redesigned, not just recoated.
Traceability and Documentation
Structural supply requires the material certificate chain and the coating records, because both feed the design calculation. Here is what can accompany an order.
- EN 10204 3.1 material certificate
- Mill certificate traceability by heat lot
- Dimensional inspection report
- Mechanical property test report
- Coating thickness measurement
- Slip coefficient test report on request
- Lot marking on parts and packaging
- Retained sample held for future comparison
Traceability runs from the incoming mill certificate through forming, heat treatment and finishing, and is recorded by lot. Where your specification calls for a particular certificate format or a slip coefficient test, send the requirement with the enquiry so we can confirm it before production.
Delivery and Trade Terms for Structural Buyers
The questions structural buyers ask before approving a new supplier, answered before you ask them.
Structural Fastener FAQs
Answers to the questions structural engineers and procurement teams ask most often, with specific values rather than general assurances.
What is the difference between a bearing type and a slip critical joint?
A bearing type joint transfers load by shear and bearing on the bolt and the plate, and the bolts only need to be snug tightened. A slip critical joint transfers load by friction between the connected plies, which requires a designed preload and a controlled coefficient of friction on the faying surface. The two are not interchangeable, and the specification of the hardware and the inspection regime follow from which one the connection is designed as.
Can I galvanize a slip critical connection?
Not over the faying surface. Slip resistance depends on a defined coefficient of friction between the plies, and a coating on that surface changes the coefficient and can remove the slip capacity the connection was designed for. The bolt, nut and washer are coated, and the faying surface is left clean and uncoated unless the design explicitly specifies a coating qualified to a slip class. Zinc flake and mechanically plated systems can be supplied to a slip class, which is why they are often used on slip critical connections.
Does hot dip galvanizing affect whether the nut will fit?
Yes. Zinc adds roughly 50 to 100 microns per surface, on both the male and the female thread, so a nut that fits on the bare thread will not assemble afterwards. The parts are either tapped oversize after galvanizing or the threads are masked during the process, and which approach applies should be agreed before the order. This is a common source of site delays when it is discovered during assembly rather than at the enquiry stage.
Which preload verification method should I specify?
Direct tension indicator washers are the most reliable on site because they verify the load directly and are not affected by friction variation. Turn of nut is simple and inexpensive but depends on a consistent snug tightness. A calibrated wrench is convenient but gives poor repeatability on coated threads, because friction varies between batches and between positions in the same joint. Follow the project specification where one exists, and use DTI washers where the preload is critical.
What grade should I use for a structural connection?
Grade 8.8 covers most general structural work, and grade 10.9 is used where a higher preload or a smaller fastener is needed. The grade alone does not make the joint safe, because the connection capacity also depends on the plate, the end distance, the edge distance and the preload. Send the connection detail and we will confirm the grade and the hardware rather than quoting from the bolt size alone.
How do I stop bolts loosening on a structure subject to vibration?
On structural connections the usual answer is designed preload rather than a locking device, because a properly preloaded joint does not loosen under transverse vibration the way a snug tightened one does. Where preload is not achievable or the joint is subject to impact, a prevailing torque locking element or a mechanical locking device is used. A structural lock washer is generally not sufficient on its own for a joint that sees cyclic loading.
Do you supply HSFG assemblies?
High strength friction grip assemblies, meaning the bolt, nut and hardened washer supplied as a matched set, are available. The set matters because the washers are hardened to avoid brinelling under preload, and brinelling is one of the mechanisms that causes preload loss over time. If your specification calls for a matched assembly, say so at the enquiry so the washers are included in the quotation.
What is thread engagement length in steel?
As a rule of thumb, one to one and a half times the nominal diameter of engagement in steel gives full bolt strength in most structural materials. Engagement is reduced where the mating material is weaker, and increased where it is aluminium or a soft casting. For structural connections the engagement is usually set by the plate thickness and the connection design rather than chosen freely, so confirm against the connection detail.
What documentation comes with structural fasteners?
An EN 10204 3.1 material certificate with heat lot traceability, a dimensional inspection report, a mechanical property test report and coating thickness measurement. Slip coefficient test reports are available on request where the connection is slip critical. Where your specification calls for a particular certificate format, send the requirement with the enquiry so we can confirm it before production.
Can you work with the quantities typical of a construction project?
Yes. Construction projects often need moderate quantities of many different parts, and single piece prototypes are accepted for machined components and cast in hardware. Low volume changes the unit cost, so the price per part will be higher than a repeat production run, but we quote the job as it is. Samples ship by air freight.
Send a Connection Detail or Drawing
One message is enough. A connection detail, a drawing reference, or a plain description of the joint is enough for us to start.
- Reply within 24 hours on working days
- Connection type confirmed before quoting
- Material certificate and coating records with supply
- Slip coefficient testing available on request