# Experimental and Numerical Analyses of Timber-Steel Footbridges
## 2 Parametric Study of Timber Footbridges  
Optimal types of timber-based bridge systems combined with a steel member deck to be used in footbridges and small road bridges were developed in cooperation with the timber bridge execution company CB Ltd. [23], which has extensive previous experience with producing similar types of structures. The parametric numerical study was focusedon timber plate-girder footbridges with bottom bridge decks consisting of appropriately combined steel and wooden members. The main girders of the investigated footbridges consisted of two plate-girders made of glued laminated timber. They were always placed at such an axial distance as to ensure a free width of 2.8 m between them. After applying two-sided curbs with a width of 150 mm, a free width of 2.5 m of the pavement was ensured. Footbridges with spans of 12, 16, 20, and 24 m were proposed. The heights of the main girders were chosen as 1/13.33 of the respective spans and were constant along the overall lengths of the girders. The thicknesses of the girders resulted from the verification of their resistance, deformation, and dynamic response. The results were gulam girders with a cross-section of 150/900 mm for a span of 12 m, 180/1200 mm for a footballer with a span of 16 m, 220/1500 mm for a span of 20 m, and 280/1800 mm for a footbridge with a span of 24 m. The main girders were designed with the pre-campering of a circular arch shape; the maximum value fell in the middle of 1/25 of the span (see Figure 1). Three types of bridge member decks were analysed. The first type was a steel member deck composed of steel cross-girders, stringers carrying the transverse wooden bridge covering and the transverse oak plank pavement, and bottom steel bracing (Figure 2). Cross-girders made of hot-rolled steel IPE 200 profiles were connected to the main girders in each span variant at axial distances of 4.0 m. The end cross-girders were made of hot-rolled profile HE200A. Two stringers made of hot-rolled steel IPE 200 profiles were connected between the cross-girders at an axial distance of 2.00 m. On the stringers' upper flanges, a bridge covering made of oak beams with a cross-section of 200/110 mm was transversely laid. The stiffness of the bridge superstructure in the transversal horizontal direction was ensured via bottom longitudinal bracing, which was designed using hot-rolled steel angles arranged in the shape of a rhombic system under the plane of the cross-girders. The second type of bridge deck was made up of the same structural elements as the first one. However, the stringers were designed from L 140 \(\times\) 140 \(\times\) 10 hot-rolled steel angles and were continuously connected with screws directly to the main girders (Figure 2). This simplified the deck, but the bridge covering, constructed using oak beams with a cross-section of 200/120 mm, contributed to the spatial effect of the overall system to a greater extent, which had to be considered in the computational model. Cross-girders and longitudinal footbridge bracings were designed with the same profiles and at the same distances as in type I. In the third type of the proposed bridge deck, the stringers were omitted entirely. A bridge covering made of oak beams with a cross-section of 200/110 mm was placed longitudinally on the upper flanges of the cross-girders, which were, therefore, all designed with the steel wide-flange hot-rolled profile HE200A (Figure 2). The axial distance of the cross-girders was 2.0 m in each span variant. An oak pavement of 40 mm in thickness was again placed on the wooden bridge covering. In this case, the bottom longitudinal bridge bracing made of angles was arranged in the form of a K-truss system. The parametric study was carried out using SCIA Engineer software ([[https://www.scia.net/en](https://www.scia.net/en)]([https://www.scia.net/en](https://www.scia.net/en)) (accessed on 5 January 2023)) [24]. The main girders made of glued laminated timber were modelled using shell finite elements.