Fixed, Guided and Free Sliding Bearings: Reading a Bearing Schedule

A bearing schedule is a map of structural behaviour

A bearing schedule should do more than list support identifiers and product labels. It is a concise map of how the superstructure transfers actions while permitting selected movement and rotation. Fixed, guided and free appear simple, but each term has meaning only when it is read with the project’s local coordinate system, bearing locations, movement arrows, reaction data and connection details. Before asking for a quote, the purchaser should be able to trace what each support is expected to restrain, what it is expected to permit and which drawing shows the relevant orientation.

The schedule does not replace structural calculations, approved drawings or project specifications. It collects their bearing-related consequences in a form that designers, fabricators, inspectors and site teams can use. If the schedule is incomplete, it should state what is provisional. A clear unknown is safer than an assumed guide direction or movement range. The outcome of reading the schedule is a better RFQ: one that carries the intended bearing function forward without turning a generic product name into an unverified solution.

Establish the axes before interpreting the labels

Every schedule should make its axes explicit. On a straight bridge, project teams may describe a longitudinal axis along the bridge and a transverse axis across it. On a curved, skewed or complex structure, local directions at each support can be different from the overall site orientation. The drawing should show how the bearing’s local direction relates to the bridge geometry. If the schedule and the plan use different conventions, resolve the difference before a guided arrangement is manufactured or installed.

Rotation should also be identified separately from translation. A bearing may need to accommodate angular change about one or more axes even when its sliding direction is limited. Likewise, the fact that a bearing is called free does not eliminate the need to state its translation envelope. Keep an axis legend with the schedule, and use the same convention in the reaction table, product drawing and installation records. This small discipline reduces the risk that an otherwise correct component is rotated, marked or compared incorrectly at a support.

For a related project route, review Pot Bearings or Spherical Bearings or PTFE Sliding Bearings in the context of Highway Bridges.

Read a fixed function as a force-path decision

A fixed bearing location is generally intended to restrain selected translation and participate in the structural horizontal-action path. The schedule should therefore identify more than the word fixed. It should show the location of the fixed point in the full bridge, the relevant longitudinal and transverse actions, the support and connection context, and any separate structural element that also contributes to restraint. A fixed point located differently in the bridge can change the movement demands at other supports, so the function belongs to the layout rather than to an isolated item.

For an RFQ, ask whether the fixed condition applies in all relevant project stages or only in the completed structure. Erection, staged construction, launching, replacement or temporary restraint can introduce additional conditions that the schedule needs to distinguish. Do not infer that a bearing alone transfers every horizontal action if the drawings show a key, stop, pin or other element. The supplier needs a clear boundary of responsibility and interface information to develop a configuration that matches the project intent.

Read a guided function as a directional requirement

A guided bearing permits movement in one declared direction while restraining the perpendicular direction through the project arrangement. The most important item is the guide direction relative to the local axes. A schedule should show a movement arrow, a labelled axis and a bearing orientation that can be checked against the plan. This is not a cosmetic drawing feature. If a guide is oriented differently from the intended path, it can conflict with expansion movement or transfer actions in an unintended direction.

The RFQ should also state the translation range, reversals, horizontal actions, rotation conditions, available travel, support geometry and construction status. On a curved or skewed bridge, take particular care with local orientation. Include the bearing location and a detail of the support interface rather than relying on a phrase such as “longitudinal guide.” Longitudinal to the bridge may not be the same as a local fabrication reference unless the drawing makes the relationship clear. When in doubt, send the schedule and plan together and identify the required movement vector directly.

Read a free-sliding function as a controlled movement envelope

Free does not mean undesigned. A free-sliding bearing still needs a declared movement plane or axes, a total travel requirement, a relationship to rotations, protection of the relevant interfaces, support clearances and a site context that permits inspection and installation. The wider bridge restraint strategy may be provided by other locations or components, but the free position must be coordinated with them. A schedule should not use free as a substitute for a movement value.

When reading the schedule, look for the project conditions behind the movement. Are temperature, shrinkage, creep, settlement or construction-stage effects included? Does travel reverse? Is there an expansion joint whose movement needs to align with the bearing arrangement? Is the support line curved or skewed? Are there stop blocks, drainage conditions or external elements that restrict the available space? These questions are not a generic design calculation; they are the missing context that turns a free label into a reviewable procurement request.

Keep rotation and restraint separate from movement labels

One frequent misunderstanding is to treat a movement function as proof that all other bearing questions have been answered. A bearing may be fixed in translation at a location while still accommodating rotation. A guided configuration may have rotation as well as one permitted translation direction. A free arrangement may need to accommodate movement in a plane while still carrying the project’s vertical actions and fitting a constrained interface. The schedule should keep translations, rotations, reactions and restraint intent in separate fields or clearly associated notes.

When an RFQ is prepared, ask for the relevant action combinations and identify whether rotation and translation occur together. State the bearing family if known, but do not use the family name to hide incomplete data. The vendor can then identify which inputs need confirmation rather than treating an ordinary label as a complete selection. This is particularly important for projects with unusual geometry, seismic demands, replacement constraints or construction stages, where the most important bearing behaviour may occur outside the simple service-state description.

Connect schedule entries to the support detail

A schedule tells the team what the bearing must do; the support detail shows where it must do it. Read both before seeking a quotation. Look for plan dimensions, available height, top and bottom levels, pedestal geometry, connection/anchor concept, hole locations, edge distances, adjacent reinforcement, diaphragms, clearances, surface conditions, installation datum and access. If a guide, connection plate, anchor or sliding component is in the intended scope, state whether it is included in the bearing request or belongs to a separate structural package.

For replacement work, add the existing support survey, bearing identifier, condition photographs, jacking/temporary-works questions and work-window restrictions. These materials do not issue a field instruction. They help distinguish what can be defined from the current record and what needs responsible project review. A quotation can then identify its assumptions rather than silently relying on a support geometry that does not exist at site.

Turn the schedule into a clean RFQ

The best RFQ attaches the bearing schedule, plan/elevation, reaction table, movement and rotation data, applicable specification, quantity and programme. It should tell the supplier which drawings are approved and which are preliminary. It should list special conditions such as uplift, temporary restraint, replacement access, unusual exposure or extra document requirements. It should ask for a clear supply boundary covering the bearing assembly, interfaces, anchors or guides where applicable, protection, inspection records, drawings, marking, packing and delivery documents.

Before release, compare every response against the same schedule entries and local axes. Check that the stated function, guide direction, movement/rotation basis, action assumptions and interface scope have not changed. This turns the schedule from a list of labels into a practical tool for technical coordination. It also keeps the final design and approval responsibility in the correct place: with the project’s controlled engineering process.