Suspension Bridges – Eliminating Bending at the Pier Base In a suspension bridge, how is bending at the base of a pier minimized or avoided by the detailing of the main suspension and anchor cables?

Introduction / Context:
Pier detailing in suspension bridges is critical to transfer cable forces efficiently. If cable forces introduce large moments, the pier base experiences undesirable bending. Properly designed saddles and bearings help align the resultant through the pier's centroidal core, reducing bending demands.

Given Data / Assumptions:

• Main suspension cable carries vertical loads to the piers and anchors.
• Anchor cables balance horizontal components.
• Roller-mounted saddles allow relative movement and load alignment.

Concept / Approach:

By seating both suspension and anchor cables over a saddle on rollers, the cable can adjust position and transmit primarily compressive resultant through the pier. The rollers allow small longitudinal movements due to temperature and live-load effects while aligning the cable's line of action with the pier centerline, minimizing bending moments at the base.

Step-by-Step Solution:

Verification / Alternative check:

Bridge practice shows roller or rocker saddles are standard at pylons to reduce fixed-end moments; finite element models confirm markedly lower base moments compared to rigid cable fixity.

Why Other Options Are Wrong:

(a) and (b) impose rigidity, inducing bending from temperature/load shifts. (d) contradicts efficient design philosophy. (e) is structurally infeasible for a suspension system.

Common Pitfalls:

Confusing anchor saddles at abutments with pylon saddles; assuming fixed connections are beneficial for stability.

Final Answer:

Attach suspension and anchor cables to a saddle mounted on rollers at the pier top so that the line of action passes through the pier and horizontal movement is accommodated