A frame structure is a skeleton of connected beams and columns that supports a building’s weight and transfers it down to the foundation. Think of it like the bones inside a body: the frame carries every load while the walls, floors, and roof attach to it. This is the most common structural system used in modern buildings, from single-story houses to skyscrapers, and it works with steel, reinforced concrete, or timber.
Beams, Columns, and How They Connect
A frame structure has two core elements. Columns are the vertical members that carry weight downward. Beams are the horizontal members that span the gaps between columns, supporting floors and roofs. Where a beam meets a column is called a joint or connection, and the behavior of that joint defines how the entire frame performs.
Floor slabs sit on top of beams. When you place furniture, people, or equipment on a floor, that weight passes into the beams, travels to the columns, continues down through every column below, and finally reaches the foundation. The foundation then spreads those forces into the ground. This chain of transfer is called the load path, and keeping it unbroken is the single most important job in structural design.
Rigid Frames vs. Braced Frames
Not all frame structures resist forces the same way. The two main approaches are rigid (moment-resisting) frames and braced frames, and the difference comes down to how they handle sideways forces like wind or earthquakes.
In a rigid frame, the joints between beams and columns are welded or cast so they cannot rotate. When wind pushes against the building, those stiff joints absorb the bending forces and keep the frame from swaying too far. Rigid frames allow wide-open floor plans because they don’t need diagonal supports cluttering the interior, which is why they’re popular in office towers and hospitals.
A braced frame adds diagonal members, usually steel rods or angles, between columns. These diagonals form triangles within the frame, and triangles are inherently stable because they can’t change shape without breaking a side. Bracing dramatically increases a frame’s stiffness and strength, making the structure far less sensitive to how the joints themselves behave. The trade-off is that those diagonal members can limit where you place doors, windows, and open corridors.
Many real buildings use both systems together. A concrete core with rigid connections might handle the center of the building while braced bays handle the perimeter, giving designers flexibility where it matters most.
Steel, Concrete, and Timber Frames
The material you build a frame from shapes nearly every decision that follows: how tall you can go, how far beams can span, how fast you can build, and what the structure costs.
Steel Frames
Steel is strong relative to its weight, so steel beams can span long distances without intermediate columns. Typical office buildings use beams that span 30 to 45 feet, creating large open floor plates. A common steel floor system pairs wide-flange beams with a few inches of concrete poured over metal decking. Steel frames go up fast because components arrive prefabricated and get bolted or welded together on site. The main drawbacks are cost (steel is generally more expensive than concrete) and fire vulnerability. Steel loses strength rapidly at high temperatures, so it requires fireproofing, usually a spray-on coating or enclosure in fire-rated material.
Reinforced Concrete Frames
Concrete frames are built by pouring wet concrete around steel reinforcing bars (rebar) inside temporary wooden or metal forms. The concrete handles compression while the rebar handles tension. Concrete is cheaper than steel in most parts of the world, and it naturally resists fire far better. A standard post-tensioned slab in a high-rise is about 8 inches thick. The downsides are heavier weight and slower construction, since concrete needs time to cure before the next floor can be built on top of it. Spans are shorter than steel, so you’ll typically see more columns in a concrete building’s floor plan.
Mass Timber Frames
Engineered wood products like cross-laminated timber (CLT) and glue-laminated beams have expanded what’s possible with wood. Updates to the International Building Code now allow mass timber buildings up to 18 stories (roughly 270 feet) when all timber elements are fully encapsulated in drywall for fire protection. Buildings up to 8 or 9 stories can leave some wood surfaces exposed. Engineers have found that mass timber combined with concrete provides fire protection equal to or better than some traditional assemblies. Timber frames are lighter than concrete, can be prefabricated for fast assembly, and store carbon rather than releasing it during manufacturing.
How Frames Handle Earthquakes
Earthquake design for frame structures centers on one idea: controlled damage. Engineers don’t try to make the frame so strong it never bends. Instead, they design specific locations, usually the ends of beams, to bend and absorb energy without collapsing.
The preferred strategy is called “strong columns, weak beams.” Columns are made stronger than the beams connecting to them, so during an earthquake the beams yield first. When beams on every floor yield at both ends, the frame forms what engineers call a mechanism, and it can sway back and forth dissipating seismic energy across the entire structure rather than concentrating damage on one floor. This spreading of damage is critical because a single weak story that collapses while the rest remains stiff is one of the deadliest failure patterns in earthquakes.
To make those beam ends ductile enough to bend repeatedly without snapping, engineers use closely spaced hoops of reinforcement (in concrete) or special detailing at welded connections (in steel). Research at the University of Memphis found that adding confining reinforcement to a concrete column more than tripled its usable bending capacity, from just under 500 microstrain per inch to over 1,600. That extra flexibility is the difference between a building that rides out the shaking and one that doesn’t.
How Frame Structures Fail
Frame failures fall into two broad categories: material failure and buckling. Material failure happens when a beam or column is simply overstressed, cracking or yielding beyond its capacity. Buckling is more sudden and often more dangerous.
Buckling occurs when a slender column under compression suddenly bows sideways. This is the same effect you see when you press down on a thin ruler stood on end: it snaps to one side long before the material itself crushes. The most common form, Euler buckling, affects long, slender columns. But frames can also experience lateral buckling in beams, torsional (twisting) buckling, and local buckling, where a thin section of a steel beam’s web or flange crumples. A general rule of thumb is that any component with a thickness-to-depth ratio below 1 to 10 should be checked for local buckling.
Joint failures are another concern. In concrete frames, the area where a beam meets a column can be subjected to intense shearing forces during an earthquake. If that joint isn’t properly reinforced, it can crack and lose its ability to transfer loads, potentially triggering a progressive collapse.
Construction Speed and Cost
One of the biggest practical advantages of frame structures is that they lend themselves to prefabrication. Steel frames arrive as pre-cut, pre-drilled pieces that bolt together. Mass timber panels are CNC-machined in a factory and assembled on site like oversized furniture. Even concrete frames can use precast columns and beams shipped ready to install.
Prefabricated steel frames require an estimated 33% less erection time than conventional site-built steel structures. Fewer pieces, less field welding, and reduced weather sensitivity all contribute to faster schedules. For the building owner, a faster frame means an earlier move-in date and lower labor costs overall. Conventional site-poured concrete, by contrast, is more exposed to weather delays and the sequential pour-and-cure cycle that limits how quickly you can move up the building.
Cost comparisons vary by region. In areas where labor is expensive and steel is readily available, steel frames often win despite higher material prices. Where labor is cheaper and cement is locally produced, concrete frames are hard to beat on price. Timber frames occupy a middle ground, with material costs that depend heavily on local supply chains but labor savings from rapid assembly.