bridges are looking elegant and aesthetically pleasing, it is only because they are designed to structural efficiency and economy, accidentally (not by intent) conforming to the principle of ‘Form Follows Forces’. Few of the aesthetically appealing bridges are analysed below for their qualitative aesthetic attributes. 4.1 Arch bridges Most of the long span bridges constructed in India up to 1950’s was of arch types, either of spandrel type arch, semi-through arch or tied arch (bow-string girders). This is author’s strong intuition that the arch bridges are most sustainable bridges as majority of the structural components in arch are axial members where the flexure is minimum. Among them the Coronation Bridge, an open spandrel arch, which is constructed in 1941 across Teesta River, Northern Bengal, deserves the special recognition. The arch span of 81.71 m with the unusual central rise of 39.63 m was constructed by suspended shuttering staying from temporary tower at the location adjacent to springing point. This durable, elegant structure has visual appeal because of its shape and also containment in the river valley with high bluff. The visual impact is accentuated by rise to span ratio conforming to golden section rule, apart from blending with the environment. The visual success can also be attributed to the fact that the arch element, spandrel columns and deck beams are dimensioned to the principle of Form Follow Forces. The main columns at the springing location enhance the containment effect. The entire structure has an artistic elegance.
45.12 m span each. The bowstrings are realized by vertical mild steel hangers. The visual impact is achieved by continuous slender tie-chord from abutment to abutment and also a smooth integration of side spans with the abutments. The key to good appearance in the bowstring girder bridge is the graceful overall shape, the minimum variety of members, simple and attractive connection details, judicious choice of materials such as concrete for arch to take compression, mild steel for hangers to take tensions and masonry pier which is predominantly subjected to vertical force. Sometimes, it is not possible to support the deck by spandrel, as in the case of Mand bridge constructed in 1946, which has a main span of 50.0 m supporting the deck at around mid rise level by hanging stringers, that can be classified as ‘semi through’ or ‘half through’ arch bridge. The latest in the family is the true arch bridge in India on NH-21 across river Beas at Ramshilla. The national highway leading to the most popular hill station Manali in Himachal Pradesh passes through congested Kullu town. The Ramshilla Bridge has a span to rise ratio of 5.7 for the arch span of 100 m. Perhaps, the aesthetic appeal of the bridge could have been accentuated by avoiding the arch being skewed to the direction of the flow of the river as well as by bringing the span to rise ratio closer to golden section rule φ4 = 6.85. 4.2 Integral & submersible bridges During 1930’s to 50’s, multi framed submersible bridges were constructed in India and functionally warranted very slender aerodynamically shaped deck as well as pier sections. These days the similar portal framed structures are being adopted for flyovers and is now called integral bridges. The Indrāvati Bridge in Orissa (Fig14) constructed in
Fig. 13 : Coronation, Ramshilla, Mand & Alwaye
The Alwaye Bridge of 1941, which is constructed across Periyar in kerala, has three tied arches with 48 Volume 45
Number 3 September 2015
Fig. 14 : Top : Indrani bridge, Bottom : Krishna bridge
The Bridge and Structural Engineer