Earthquake & Seismic Design Fundamentals
to Eurocode 8 (EN 1998-1)

1. Elastic & Design Response Spectra (EN 1998-1)

Eurocode 8 Part 1 (EN 1998-1) defines seismic action using elastic response spectra parameterized by peak ground acceleration a_g, soil factor S, and corner periods (T_B, T_C, T_D). For ground types A through E, the horizontal elastic spectrum S_e(T) is evaluated across structural period range T.

To reduce linear elastic forces by allowing energy dissipation through plastic hysteresis, the design spectrum S_d(T) is obtained using behavior factor q:

2. Behavior Factor (q) & Ductility Classes

Eurocode 8 classifies buildings into three Ductility Classes depending on structural dissipation capacity:

3. Lateral Force Method of Analysis

For regular structures meeting fundamental period criterion T₁ ≤ min(4T_C, 2.0 s), the total base shear F_b is computed as:

Where total mass m = ∑ [G_k,j + ψ_2,i · Q_k,i] and mass correction factor λ = 0.85 (for T₁ ≤ T_C with > 2 storeys) or 1.0.

The base shear is distributed along the height proportional to floor mass m_i and elevation z_i:

4. Capacity Design & Drift Limits

To prevent brittle shear failure in columns before plastic hinges form in beams, capacity design criteria govern column design resistance M_Rc:

Interstorey drift d_r under damage limitation requirement must satisfy d_r · ν ≤ 0.005 h for buildings with non-structural elements fixed in a way as not to interfere with structural deformations.

Seismic Design Rules

1. 1

   Regularity Check

   Ensure structural plan and elevation regularity to minimize torsional amplification.

2. 2

   Ductile Detailing

   Provide closely spaced confinement links (≤ 100 mm spacing) in critical primary plastic hinge zones.

3. 3

   Second-Order (P-Δ) Effects

   Verify interstorey drift sensitivity coefficient θ = (P_tot · d_r) / (V_tot · h) ≤ 0.10.