Building in seismic zones: what the codes require, from Bali to Europe

Key facts

• Indonesia mandates SNI 1726:2019 (Badan Standardisasi Nasional), built on the 2017 national seismic hazard map; the Ministry of Public Works (PUPR) publishes the official site-specific response spectrum tool.
• Europe designs under Eurocode 8 (EN 1998), with national annexes per country.
• Both codes converge on the essentials: the site governs (soil class, spectrum), geometry protects (regularity in plan and elevation), ductility saves (dissipating energy rather than resisting head-on).

Why does the same earthquake cause different damage?

Because soil amplifies or dampens. A soft sedimentary deposit can multiply the accelerations felt by the structure; sound rock transmits them without amplification. That is the first thing a seismic code requires: classify the site's soil, then derive a response spectrum — the curve telling the engineer which accelerations the building must absorb at its natural period. In Indonesia, that spectrum is obtained officially from the PUPR application.

What does SNI 1726:2019 actually require?

Three families of requirements. First, categorisation: building use (a clinic is not allowed the same margins as a warehouse), site class, seismic design category. Second, configuration rules: irregularities — soft storeys, eccentric masses, abrupt setbacks — are penalised or prohibited, because earthquakes seek them out. Third, ductility requirements: reinforcement detailing, beam-column joints and anchorage lengths that let a building deform without breaking.

How does Eurocode 8 differ?

In philosophy, very little: EN 1998 relies on the same spectra, the same soil classes, the same "strength or ductility" hierarchy. The difference is institutional: each member state sets its parameters in a national annex. That is why designs are never "copied" between countries — the code is shared, the values are local.

What this changes for an investor

A well-run tropical worksite shows itself in simple things: a dated, signed geotechnical study, drawings that cite SNI 1726:2019, an independent inspection office, logged concrete tests. Nothing spectacular — documentary discipline. That is what we require before the first formwork, and keep requiring throughout execution — our tropical worksites tell that story from the inside.

General information on construction principles. This is not an engineering study: every structure calls for a licensed engineering office and the codes in force in its jurisdiction.