Eurocode — Box Culvert Design Calculations

2.05m.

The fourth barrier landed. The total downward force crossed her calculated threshold. The culvert settled back with a wet, sucking sigh.

“It’s not passing,” Elara shouted back, shoving her tablet in his face. “Look. The ULS check fails. The uplift force is 1,230 kN. Our dead weight is only 1,130 kN. The factor of safety against flotation is 0.92. In two hours, when the water hits 2.1 meters, this thing becomes a boat.”

Elara grabbed her high-vis jacket, a flashlight, and her tablet, which held her last, desperate design: a set of 450mm thick wing walls that would anchor the culvert to the dense clay. But she hadn’t finished the checks. The shear reinforcement in the walls—the “stirrups”—had to resist a factored shear force of 312 kN. Her rebar spacing of 150mm gave a VRd,c (shear resistance without shear reinforcement) of just 198 kN. She needed vertical links. Expensive ones. The kind Derek had laughed at. box culvert design calculations eurocode

Her calculation showed a stability ratio of 0.92. Below 1.0.

She had also calculated the crack widths. Under the extra load, the cracks in the roof would open to 0.35mm—within EC2’s exposure class XC4 (cyclic wet and dry). It wouldn’t leak. Not yet.

Her boss, a man named Derek who believed any problem could be solved with a bigger pump, had dismissed her concerns. “The Eurocode is a suggestion, Elara,” he’d said, flicking a coffee stain off his tie. “Just shove some shotcrete on the soffit and sign it off.” The culvert settled back with a wet, sucking sigh

But then it stopped.

Water wasn’t flowing through it. It was piling up . A dark, swirling lagoon was forming behind the embankment. The old structure was acting less like a conduit and more like a dam. A crack had opened in the crown—a tension crack from negative bending moment she had predicted three weeks ago.

Derek just shook his head and walked back to his car. He never understood. The ULS check fails

Elara ignored them. She watched the water level on her laser measure. It was rising: 1.9m… 2.0m… The calculated flotation threshold.

She had already factored the permanent actions: the 1.2 meters of saturated backfill above the roof slab (γG = 1.35), the weight of the precast concrete itself (γG = 1.35), and the variable traffic load from the highway above (LM1: tandem system and UDL, γQ = 1.5). The numbers danced in a grim waltz. The design bending moment at the crown was 487 kNm.