Living With a Column Grid

A column gathers load from the beams, slabs or roof members it supports and delivers it as a concentrated force to whatever is beneath, which may be another column, a transfer element, or a foundation. Load arriving at points rather than along a line is what separates a framed building from a load-bearing-wall building, and it is the whole reason the walls can be open.

So the grid is not an obstruction to a plan. It is the thing that bought the plan its freedom everywhere else, and it is worth reading that way before it is fought.

In a steel frame the connection type decides the behaviour. Joined so that the beam ends can rotate, the frame leans on something else for stability; joined so that beam and column hold their angle, the frame resists sway itself. Replace one with the other and the forces travel differently everywhere, not only at the joint that changed.

In a cast concrete frame the elements are not connected to one another at all, they are continuous with one another, and force redistributes through the junctions rather than stopping at them. Either way, what the joints are doing cannot be read from the room.

Every column is carrying load, but some are carrying more than that. A column that also forms part of a braced bay, or that stands at the end of a transfer element, or that sits in a core resisting horizontal action, is holding work that would have to be picked up somewhere else entirely.

The published records give the tests. Ask whether stability comes from bracing, a core, or the connections themselves, and where those elements sit in plan. Ask what restrains the column laterally along its height. Ask what it is bearing on, and whether that support settles differently from its neighbours.

A column delivers a large load over a small area, and a base plate spreads that over an area the foundation can accept while providing the means by which the column is held in position. Whether that base is designed as pinned or fixed changes the forces throughout the column and the frame above it, which means a base is not a detail that follows the decision; it is part of it.

Below that, the foundation was arranged for a point of load in a position. Moving the point does not move the foundation, and column foundations are considered together rather than individually because adjacent supports settling by different amounts affects everything spanning between them.

Bracing only works if the floors can feed it. Horizontal force arrives across a whole facade and has to be collected by the floor plate and delivered to the braced bay, so a large stair opening, a riser or an atrium cut through that plate interrupts the delivery route while the bracing itself is unchanged and the frame behaves differently.

That is why a fit-out proposal to open a floor, or to place a stair in a convenient position, belongs in the same conversation as the columns. In a portal frame the equivalent is a wide door cut into what may be the only braced bay on that side.

Where the envelope meets the frame there is a bracket, and that bracket has several duties at once: it carries cladding load back into a structure that moves under wind and load, it passes through whatever is controlling water and air, and it is a metal path across the insulated line. Deciding it settles a structural, a weathering and a thermal question in the same detail.

The steel frame entry is direct about the consequence of leaving those attachments late. Drilling or welding to a frame afterwards affects both the member and its protective treatment, so late requirements are disruptive out of proportion to their size.

Grids reward plans that use them. Circulation, services risers, cores and storage all sit comfortably against columns, while rooms that need an uninterrupted centre do not. Putting the inflexible things where the structure already is buys uninterrupted space where it is actually wanted.

It also helps to name which columns are expressed and which are concealed, early. A column inside a partition line disappears; a column standing free in a room is a piece of the design whether or not anyone treated it as one.

Hanging something from a frame joins the load path just as much as removing something from it. The portal frame entry names hoists, inserted platforms, plant on the rafters and wide doors together, because each delivers its effects into members already working over their full length, and because the bracing that served a position may sit in another bay altogether.

The steel frame entry records the related misunderstanding: adding a mezzanine is described as independent, though it loads existing columns and can alter how force reaches the bracing.