Earthquake-resistant building

The question we meet most often in the rebuilding process in Hatay is this: “Is masonry safe?” The answer is not a single word. A masonry building is safe if its load-bearing walls are confined by reinforced concrete elements; if they are not, it is not. Most of the buildings that collapsed in February 2023 belonged to the second group.

We prepared this page to fill a gap we keep running into while working with historic buildings: owners are forced to make decisions without understanding how the system works. The eight steps below are not a technical specification but a reading guide to what is done on site and why. Their purpose is to let you follow your own project and its construction with the right questions.

The roadmap

What does earthquake resistance mean?

Let us begin with the most important sentence on this page: there is no such thing as a fully earthquake-proof building. Any structure may meet a shaking stronger than the one it was designed for. The purpose of earthquake engineering is not to eliminate damage but to prevent collapse.

Codes describe this as performance levels. In small, frequent earthquakes the building should remain undamaged; in a large, rare one it may be damaged, even beyond repair — but it must stay standing and allow those inside to evacuate. Life safety comes before the protection of property.

Knowing this sets the right expectation. The conclusion “there was an earthquake, my house has cracks, so it was badly built” is often wrong. The right question is: where is the crack, in which element, and has the structure kept its integrity? Only an inspection on site can answer that.

Six principles

Regular form. Simple geometry in plan and section. Complex, asymmetric or projecting shapes twist the building and create concentrations of force at corners that are hard to resist. An irregular mass can be divided by joints into several regular ones.

Lightness. The lighter the building, the smaller the force acting on it, because that force is proportional to mass. Unnecessary weight is avoided especially on upper floors and at roof level.

Adequate stiffness. In a building that flexes too much, non-structural elements — walls, glazing, services — are damaged. Lateral drift must be limited.

Sound foundation. Differential settlement can crack a building under its own weight alone. The soil survey and the choice of foundation type matter as much as the superstructure.

Vertical continuity. Structural elements must run without interruption from foundation to roof. A wall that disappears for one storey has nowhere to pass its load.

Sound materials. The building must be able to absorb the energy the earthquake delivers. Brittle, low-strength or untested material destroys that capacity from the outset.

What is confined masonry?

Confined masonry is the system in which the load-bearing wall is built first and reinforced concrete vertical and horizontal ties are then cast around it. The order matters: the wall is laid first, the concrete poured afterwards. The concrete then keys into the toothed face of the masonry and the two behave as one.

In a reinforced concrete frame the opposite happens: columns and beams are cast first and the wall is built afterwards as infill. There the wall is not load-bearing. Mixing the two systems — starting like a frame and finishing like masonry — is the most common and most dangerous error on site.

The purpose of confinement is not to carry load but to hold the wall together. During an earthquake the wall will crack; the tie prevents that crack from growing into a collapse. The tie protects the wall not from cracking but from falling apart.

Why does it work?

Masonry is very strong in compression and almost powerless in tension. An earthquake applies a horizontal force that puts the wall into tension; an unconfined wall breaks and topples at that point.

A reinforced concrete tie adds tensile capacity around the wall. It is like tying a stack of books with rope: when you push it, the books slide over one another and take damage, but they do not scatter across the floor. In a building, that difference is the time the occupants have to get out.

This is why confinement must exist around every wall panel, not only at the corners. A wall left free along one edge is a stack of books with one end of the rope untied.

Steps 1–2: Site and plan layout

The soil is part of the building. Fill sites, former landfill, stream beds, landslide zones and positions leaning against a retaining wall are avoided. On sloping ground the building sits on stepped foundations; construction is never carried out on a sloping foundation. All of this is settled by a geotechnical survey — the survey is not a formality but an input to the project.

Three principles govern the plan. First, proportion: the length of the building should not exceed three times its width. Second, symmetry: load-bearing walls should be distributed evenly in both directions, and the centre of mass should sit close to the centre of rigidity; otherwise the earthquake twists the building.

Third, solid walls: every facade must carry at least one load-bearing wall without large openings. Turning an entire street facade into shopfront glazing destroys the building’s resistance in that direction — one of the most common collapse patterns in earthquakes.

A simple mass is preferred to a complicated plan. Where a complex form is unavoidable, the building is divided by seismic joints into independent simple masses, each with its own confinement.

Steps 3–4: Foundation and masonry

The foundation is excavated down to firm ground and runs continuously beneath every load-bearing wall. Foundation beams tie the building together like a box; wherever they are interrupted, the building begins to behave as two separate parts. Service pipes are not run through the foundation or the ties but pass through openings left in advance.

The fundamental rule of masonry is interlock: vertical joints must not line up, and each course should be offset from the one below by at least a third of a brick. Aligned joints amount to a ready-made split in the wall.

Mortar quality is often underestimated, yet it governs the strength of the wall. Joints must be full, their thickness kept regular, and the bricks wetted before laying; dry brick draws the water out of the mortar and leaves it weak.

The ends of the wall where it meets the tie are left toothed. Concrete poured against a flat face does not key into the wall, it merely leans on it — and performs no confining function. This detail is the one most often skipped on site, and it directly determines whether the system works.

Steps 5–6: Vertical and horizontal ties

Vertical ties are placed at both ends of a wall, at corners, beside openings and at set intervals; the spacing is determined in the project according to the span the wall can carry. Horizontal ties run at every floor level, and between floors where required, closing around the building at each level.

Confinement is not complete until the two are joined. The reinforcement of the vertical tie enters the horizontal tie, and that of the horizontal tie the vertical, over an adequate lap length. Ties cast separately and left unconnected are merely pieces of concrete.

Stirrups hold the vertical reinforcement together and stop the concrete from bursting apart. Their ends must be bent inwards; a hook turned outwards opens during shaking and the stirrup loses its function. Stirrups are spaced more closely towards the ends of a tie, because damage begins there first.

Door and window openings deserve particular care. Every opening is framed by a tie band above and below and vertical reinforcement on both sides. The corners of an unframed opening are the first place a crack starts in an earthquake.

Steps 7–8: Slab, roof and inspection

A slab is not merely a surface to walk on but a diaphragm tying the building together horizontally. A reinforced concrete slab distributes the earthquake force among the walls, which is why it must be continuously connected to the ties. In timber or steel floors that connection is resolved separately.

The vertical continuity of load-bearing walls is decisive here: beneath every wall there must be a corresponding wall on the floor below. A wall present upstairs with no counterpart below transfers its load into thin air — one of the main causes of the “soft storey” collapse that takes the most lives in earthquakes.

Lightness matters at roof level. A heavy roof means a large inertial force at the top of the building. The roof structure is anchored to the ties; a roof merely resting on the wall slides under horizontal force.

The last step is inspection, and it really begins at the outset. In Türkiye the building inspection body must see the reinforcement in place before the concrete is poured. Documenting every stage with photographs is both a legal requirement and a record for the building’s future. You cannot look inside a tie once it has been cast.

Regularity in elevation and the soft storey

Regularity in section matters as much as regularity in plan. An abrupt change of stiffness or mass between storeys makes the earthquake energy pile up in a single floor. That floor drifts far more than its neighbours, and it fails first.

In Türkiye the best-known version of this is the soft storey: walls removed at ground level so the space can become a shop, a car park or an entrance hall. The floors above behave as a stiff block while the ground floor is left standing on slender columns; under shaking that storey leans over and the building sits down on it. It was one of the most common collapse patterns in February 2023.

The same problem arises in reverse: a heavy terrace, a water tank or a storey added later carries mass to the top and increases the overturning effect. The rule is simple — floor plans and wall layouts should resemble one another, and the weight should stay low.

Seismic joints and additions to an existing building

Every building has its own rate of oscillation, set by its mass and stiffness. Two buildings standing side by side swing at different rates. If there is not enough space between them they strike each other during an earthquake — this is called pounding, and it usually leaves both structures more heavily damaged than expected.

For this reason a seismic joint is left between adjoining buildings and wherever an irregular mass is divided into parts. The width of the joint increases in proportion to the height of the building and, in Türkiye, is calculated according to the rule set out in TBDY 2018. The joint runs from the foundation upwards where required; it must stay permanently empty and must never be filled with mortar or rubble.

A situation we meet often in Antakya is an addition to an existing building: enlarging a kitchen, adding a room, closing off a facade. The rule here is this — the addition must either be built in the same structural system as the main building and tied to it, or be entirely separated and stand on its own structure. The halfway solution is the worst of all.

Mixing materials of different stiffness — adding a reinforced concrete room to a masonry house and gluing the two together — guarantees damage at the junction. The two systems behave differently, the junction is left to carry that difference, and it tears there first.

At which stage is the failure born?

Ten months after the earthquake, a field study in Kırıkhan, Antakya, Defne and Samandağ examined the collapse patterns of heavily and moderately damaged buildings in situ. Its findings do not reduce to a single cause; they show that failure can be born at four separate stages across a building’s life.

These observations come mainly from reinforced concrete frame buildings — the dominant type in the city centre. That is a different system from confined masonry, but the logic of the stages works the same way in any system, and it determines where you, as an owner, should ask what.

The design stage. The placement of vertical structural elements in plan is decisive: when the centre of rigidity moves away from the geometric centre, the earthquake twists the building. To this are added the soft storey, the short column, wide cantilevers and the absence of a joint with the neighbouring building.

The construction stage. The most common error the study underlines is a simple one: extra water added to make the concrete easier to work on site. A mix that leaves the batching plant at the specified strength never reaches the calculated strength after that intervention. This is where the gap between the calculation on paper and the reality on site opens up.

The inspection stage. Cables, junction boxes and conduits set into columns and beams while services are run reduce the structural section directly. Once the concrete is poured these become invisible; they can only be prevented by inspection before casting.

The occupancy stage. The gravest is here. Cutting a load-bearing column or wall to enlarge a space after handover is documented in the study through many examples that led to collapse. In a shop in Kırıkhan, behind a fallen suspended ceiling, a cut column stub was found hanging 25 centimetres from the slab.

The short column: the trap that goes unnoticed

The short column is among the easiest errors to miss in design, because on the drawing the column is of normal length. The problem is born in the infill wall built beside it.

Basement band windows, half-height walls or floors stepping on sloping ground grip part of the column. The column can then flex not along its whole length but only along the short free portion left to it. When the same lateral drift must be absorbed over a very short length, the shear force in the column multiplies, and it fails by fracturing rather than bending.

The remedy is not to thicken the column but to separate the infill wall that grips it from the structure. A flexible joint is left between wall and column so that the column stays free along its whole length. This detail must be shown in the project and its execution checked on site.

The cut column and the chain of responsibility

Cutting a column means severing the building’s load path. The weight of every floor above was descending to the ground through that column; once it is cut, the load piles onto neighbouring elements or has nowhere to go at all. That is the first point to fail in an earthquake.

This is not only a technical error. Unauthorised changes made after the occupancy permit fall outside inspection, and sit unseen for years behind a suspended ceiling or a plasterboard lining.

The study does not lay the problem at one actor’s door but describes a chain of five links: the owner who wants more floor area; extra storeys granted by council decisions taken by people from unrelated professions, and unsuitable land opened to development; the craftsmen and workers who do not build to the project; inspection firms that sign for sites they never visited; and the occupant who cuts a structural element after handover.

We have not set this list out to look for someone to blame. Knowing which link of the chain you stand in as an owner also determines the questions you can ask: who drew the project, who inspected it, where is the concrete strength report, what was changed in the building afterwards. A building that has answers to those questions is safer than one that does not.

The eight errors we see most often on site

• Casting the columns firstIn confined masonry the wall is laid first. If the concrete is cast first there is no keying, and the system becomes neither frame nor masonry.
• Leaving the wall end flatIf the end that meets the tie is not left toothed, the concrete does not key into the wall but merely leans against it.
• Bending stirrup hooks outwardsA hook turned outwards opens during shaking; the reinforcement bursts apart and the tie loses its function.
• Turning a whole facade into openingsEvery facade needs at least one load-bearing wall without large openings. A shopfront facade reduces resistance in that direction to nothing.
• A wall upstairs with nothing beneath itA load-bearing wall must run from foundation to roof. Otherwise the load is transferred into thin air; this is how a soft storey forms.
• Running pipes through the tiesTies and foundations are not broken open for services. Crossings are made through openings left before casting.
• Weak mortar and dry brickDry brick draws water out of the mortar. Joints must be full and of regular thickness, and bricks wetted before laying.
• A heavy roof and an untied slabThe roof should be light and anchored to the ties. If the slab is not connected to them it does not act as a diaphragm.

Frequently Asked Questions

Sources and scope

This page draws on international field guides for confined masonry (Confined Masonry Network, EERI), on the earthquake-resistant housing guide of the Colombian Association for Earthquake Engineering (AIS), and on TBDY 2018 (the Turkish Building Earthquake Code), in particular Chapter 11 on Masonry Building Structural Systems. The field observations of failure patterns are drawn from Mıstıkoğlu, G. (2024), “Evaluation of the Problems Caused by the February 2023 Earthquakes in Hatay”, Kent Akademisi, 17(4), 1211–1230, DOI: 10.35674/kent.1486592, an open-access peer-reviewed article. Numerical values from foreign sources are not binding in Türkiye; this page conveys the principles and deliberately omits dimensioning. The text and diagrams were prepared originally by YOY Mimarlık.

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