What Is the Difference Between ASCE 41 Tier 1, Tier 2 and Tier 3?

ASCE 41 is a standard developed in the United States for the seismic evaluation and retrofit of existing buildings. It serves a purpose similar to the existing-building performance assessments carried out in Türkiye under TBDY 2018. Tier 1 is the stage at which the building's basic characteristics are examined through checklists and simple engineering calculations. Tier 2 is the stage at which the potential deficiencies identified in the first stage are assessed through more detailed checks. Tier 3 is a systematic performance assessment covering the building as a whole. In terms of the scope of investigation, Tier 3 can be likened to the detailed performance assessment level in TBDY; the calculation and acceptance rules of the two standards, however, are not identical.

The purpose of this tiered structure is to complete the assessment without entering into unnecessary advanced analysis and cost where the adequacy of the building for the selected performance objective can be understood through simpler checks. Where Tier 1 or Tier 2 does not produce a sufficient conclusion, the investigation is deepened. This avoids carrying out detailed work of the same scope on every building from the outset. That said, the building types and conditions to which these tiers may be applied are limited in the standard; for some buildings a Tier 3 assessment may be required directly. Which tier is appropriate is decided by a specialist engineer in light of the characteristics of the structure and the purpose of the assessment. ASCE’s evaluation tiers.