EN 1998-1 Seismic Base Shear Calculator

Xponexus Engineering Seismic analytics lab

Live calculation

Seismic weight W kN

Fundamental period T₁ s

Reference PGA a_gR

Importance γ_I –

Behaviour factor q –

Spectrum type EN 1998-1

Ground type (Table 3.2)

ARock / very stiff

BStiff soil

CDeep deposits

DSoft soil

EVery soft / alluvium

Uses EN 1998-1 style design spectrum: a_g = γ_I · a_gR, S, T_B, T_C, T_D from ground type, elastic spectrum S_e(T) and design spectrum S_d(T)=S_e(T)/q. Base shear: V_b = λ · S_d(T₁) · m, with λ ≈ 0.85 for long-period buildings (T₁ > 2T_C).

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Results

Design base shear and key spectrum ordinates at T₁.

Design base shear

                –
                kN
              
                Seismic coefficient Vb/W
              
                –
              
            Vb based on design spectral acceleration Sd(T1).
            Ground A · Type 1

Design PGA a_g

–m/s²

Elastic S_e(T₁)

–m/s²

Design S_d(T₁)

–m/s²

Design S_d(T₁)

–g

The values above correspond to the design spectrum at the given fundamental period. For multi-mode analyses, use the full spectrum S_d(T) across the relevant period range.

Parameter	Symbol	Value	Unit
Reference PGA	a_gR	–	g
Importance factor	γ_I	–	–
Design PGA	a_g	–	m/s²
Ground factor	S	–	–
Corner period T_B	T_B	–	s
Corner period T_C	T_C	–	s
Corner period T_D	T_D	–	s
Behaviour factor	q	–	–
Fundamental period	T₁	–	s
Lambda factor	λ	–	–
Seismic mass	m	–	tonnes
Base shear	V_b	–	kN

Base Shear & Spectrum

Results