Tool 18 · AASHTO LRFD Art. 3.6.1

HL-93 Moment & Shear Envelope

Per-lane HL-93 envelopes on simple and 2–3-span continuous girders (constant EI): design truck (35/145/145 kN, variable 4.3–9.0 m rear spacing, both directions), design tandem (2 × 110 kN), 9.3 kN/m lane load on adverse regions only, IM = 33% on axle loads, and the 90% two-truck + 90% lane case for negative moment (Art. 3.6.1.3.1). Influence lines are exact — Hermite beam elements, loads traversed node by node.

Spans

Interior supports are continuous (no hinges). Constant EI assumed — envelopes are EI-independent only for the simple span.

Key values per lane · incl. IM

These are per-lane values. Multiply by the girder distribution factor from the DF tool to get per-girder demand. The two-truck case is applied to the negative-moment envelope only, per Art. 3.6.1.3.1 (it also governs interior-pier reactions, not shown). Indicative preliminary values only — not a substitute for detailed design.

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