Granite Façade Calculation in Seismic Zones: TBDY-2018 and Anchor Design

Chapter 14 of TBDY-2018 covers 'Non-Structural Architectural and Mechanical Elements', under which granite and marble façade claddings are classified. Under the regulation, the seismic design force (Fp) for non-structural element design is:

Fp = (Sds × Wp × ap × (1 + z/H)) / (Rp / Ip)

Where: Sds = short-period design spectral acceleration coefficient; Wp = element weight; ap = element acceleration amplification factor (typically 1.0 for granite façades); z = height of the element in the structure; H = total building height; Rp = element ductility coefficient (2.5–3.5 for mechanically anchored façades); Ip = element importance factor (1.0 for standard buildings, 1.5 for critical facilities).

The practical implication: seismic design forces on façade elements installed at upper floors can be 3–4 times higher than those on elements at ground level.

Anchor points carrying each panel in a mechanically anchored granite façade must be sized to carry both permanent loads (panel weight) and transient loads (wind + seismic).

Standard 3 cm thick granite slab (unit weight 2,700 kg/m³): panel weight per m² ≈ 81 kg/m².

A 60×90 cm panel with 4 anchor points — characteristic load per anchor under weight + wind + seismic combination: typically 2.0–4.5 kN.

When TBDY-2018 Chapter 14 coefficients are applied under the seismic load combination, the typical seismic design anchor force for Sakarya (Seismic Zone 1) rises to 2.2–3.5 times that of the standard gravity calculation.

The undercut anchor (keyed mechanical anchor) — the most reliable anchor type for mechanical façades — is tested under ETA (European Technical Assessment) and ETAG 001.

Seismic performance advantages of undercut anchors: mechanical interlock working principle with no adhesive or resin dependency; compliance with seismic load categories C-1 or C-2 (documented by ETA certificate); slot working principle that permits horizontal movement, allowing the system to adapt to building deflection.

Sipahi Marble uses ETA-certified undercut anchor systems from Hilti or Fischer on all façade projects. SS316 stainless steel anchors are preferred for Sakarya projects due to their corrosion resistance against the region's humidity and salt-laden air.

The load-bearing frame of a granite façade system (aluminium or stainless steel profiles) must be able to move compatibly with the primary structural system during seismic deflection. This requires:

Vertical profiles must be fixed to the wall with slot connections that permit horizontal movement.

Horizontal supports carrying panel weight may use rigid connections — however, a minimum horizontal free-movement clearance of ±25 mm must be maintained.

At building movement joints between adjacent structural blocks, a façade expansion joint must be designed, with a 20–30 mm open gap left between panels.

The 1999 Marmara Earthquake provided the sector with direct, concrete lessons on façade cladding damage in Sakarya. Field observations from that event showed:

Adhesive façade systems: severe loss and fall risk at all locations.

Mechanically anchored façades (the rare few): largely remained in place, independent of structural damage to the building.

Impact on current practice: every mechanical façade project in Sakarya now begins with a façade drawing signed by a structural engineer. Sipahi Marble applies this rule without exception on all projects.

1. Site and soil class determination: TBDY-2018 Chapter 2 — the site's PGA (Peak Ground Acceleration) value is established. For Sakarya, Sds ≈ 0.9–1.2 g.

2. Panel dimension and weight calculation: m² panel weight and total façade surface area.

3. Wind load calculation: regional wind speed and building exposure category under TS EN 1991-1-4.

4. Seismic force calculation: Fp using the TBDY-2018 Chapter 14 formula.

5. Anchor selection and verification: design resistance (Rd) from the selected undercut anchor's ETA certificate table vs. calculated design force (Fp) — condition Rd ≥ Fp must be satisfied.

6. Structural engineer sign-off: façade project drawings and calculation report are signed and stamped.

Dynamic testing of façade systems is carried out under ETAG 034 and EOTA TR 040. These tests cover:

Anchor shear and pull-out resistance under simulated seismic loading.

Anchor fatigue resistance under cyclic loading (50 cycles).

All tests are performed in an accredited laboratory and the results are documented in the ETA certificate.

Sipahi Marble's façade systems use ETA-certified anchor and profile sets. We can provide ETA certificates and test reports on request.

In 1,000+ stone façade projects across Sakarya and surrounding provinces, Sipahi Marble provides the following contributions to the engineering process:

Seismic risk class identification at project inception.

Structural engineer coordination for façade load calculations.

Selection and procurement of ETA-certified anchor systems.

CNC anchor channel routing in the workshop (undercut channel alignment and depth under precision control).

Technical supervision during site installation.

Structural-engineer-signed conformity report on project completion.

At project start: confirm site PGA value and soil class; calculate TBDY-2018 Chapter 14 Fp; select ETA-certified undercut anchor.

During design: structural-engineer-approved façade project; CNC control of anchor channel depth and alignment; technical supervision during site installation.

On completion: sign and file conformity report; agree maintenance protocol (anchor inspection every 5 years is recommended).