Bridge Engineering Sketch

Age / Group: Ages 10+; school groups, STEM clubs, family challenge

Duration: 45–60 minutes

Objectives

• Identify the key structural components of the Maxdale Bridge: deck, abutments, span, supports, and railing

• Understand and illustrate the basic forces acting on a bridge: load (gravity), compression, and tension

• Compare the Maxdale Bridge's historical construction to modern bridge engineering principles

• Complete an annotated engineering field sketch of the bridge with labeled components and force arrows

Materials Needed

• Field journal or blank paper on a clipboard (strongly recommended)

• Pencils and eraser; colored pencils (optional, for force arrows)

• Ruler or straightedge

• Engineering vocabulary reference card (provided by MNCA or group leader)

• Tape measure or pacing cord (optional, for estimating span)

• Camera for reference photos (optional)

🪜 Step-by-Step Activity

1. Approach the Maxdale Bridge and stop at the designated safe observation area. Do not climb on, step onto, or touch the bridge structure without explicit authorization from an MNCA coordinator. Take a full 60-second observation before drawing anything.

2. Sketch the overall silhouette of the bridge as viewed from the riverbank. Use light pencil strokes — this is your working draft, not a finished drawing. Capture the shape of the span, the height above the river, and the bank geometry.

3. Label the visible structural components using your engineering vocabulary reference card. Aim to label at minimum: deck (the road surface), span (the horizontal distance crossed), abutment (the structure where bridge meets land), railing, and any visible piers or supports.

4. Draw force arrows on your sketch to show where compression forces act (pushing inward or downward — typically in the deck and abutments) and where tension forces act (pulling outward — typically in tie rods or cables, if present). Use a color code or label the arrows clearly.

5. Estimate the bridge's span length by pacing across the equivalent distance along the riverbank, or using your tape measure. Record your estimate in feet or meters next to the sketch.

6. Note the materials you can identify from observation: stone, concrete, steel rebar, timber, iron railing. Record each material and note where it is used on the structure.

7. Research or discuss with your group: When was the Maxdale Bridge built? What was its original purpose — foot traffic, wagon crossings, vehicle use? How has its use changed?

8. On a new page, design your own improved bridge for the same Lampasas River crossing. Sketch it using the same components and label what materials you would use and why. Consider: flood resilience, modern traffic loads, historic character.

9. Write a 2-sentence engineering rationale below your design sketch: What is the most important structural improvement you made, and what engineering principle guided that choice?

💬 Discussion / Reflection Questions

1. What forces does a bridge over the Lampasas River need to resist — not just everyday loads, but also periodic flooding, thermal expansion, and decades of use?

2. How has bridge-building technology changed since the Maxdale Bridge was first constructed? What can modern engineers do that earlier builders could not?

3. What materials would you specify for a new bridge at this crossing today, and what would guide your material choices — cost, durability, aesthetics, or historic compatibility?

4. If you were the engineer responsible for preserving the Maxdale Bridge, what would be the first repair you would make, and why?

Learning Outcomes

Participants apply engineering vocabulary to accurately describe real structural elements visible on the Maxdale Bridge from their field observation.

Participants demonstrate understanding of compression and tension forces by illustrating them correctly on an annotated structural sketch.

Participants practice design thinking by proposing a documented, evidence-based bridge improvement with a written engineering rationale.

Leave No Trace / Stewardship Reminder

• Observe the bridge from designated safe areas only — do not cross onto the structure without authorization.

• Do not climb on, carve into, or disturb any element of the historic bridge.

• Photograph rather than touch fragile or corroded structural elements.

• Report any observed structural damage or graffiti to the MNCA coordinator.

Engineering Vocabulary Quick Reference

Term Definition Where to Look: on the BridgeDeck The surface that carries traffic or foot loads across the spanThe top, horizontal surface you walk or drive onSpanThe horizontal distance between two supportsThe open distance above the river channelAbutmentThe structure at each end that anchors the bridge to the bankWhere the bridge meets the ground on each sideCompressionA force that pushes or squeezes material togetherActs on columns, piers, and the deck under loadTensionA force that pulls or stretches material apartActs on tie rods, cables, or the underside of a beam under loadLoadAny weight or force the bridge must carry (traffic, wind, its own weight, flood pressure)Applied from above and from river current below