**9. Maintenance issues for stone-masonry bridges**

A strikingly different bridge response and damage potential are observed when Konitsa Bridge is subjected to an excitation with the 0.19-g normalized 1940 El-Centro earthquake, which represents a different type (far-field) of seismic event lacking that characteristic dominant velocity pulse (**Figure 29**). **Figures 47** and **48** clearly demonstrate the different damage potential of this type of earthquake on such relatively long-span stone-masonry bridges. **Figure 47** depicts the Konitsa Bridge out-of-plane displacement response when subjected to PGAadjusted (0.19-g) 1940 El-Centro earthquake. **Figure 48** depicts the variation of tensile stresses together with relevant non-linear deformations of large amplitude at critical locations of the main arch during certain time windows of the response when these deformations are maxi-

**Figure 48.** Evolution of damage resulting from the El-Centro (0.19-g) far-field-type earthquake. (a) Time = 2.32 s, (b)

3.4 s, (c) 3.6 s and (d) 3.8 s.

120 Structural Bridge Engineering

**Figure 47.** Konitsa Bridge out-of-plane displacement response to PGA-adjusted (0.19 g) 1940 El-Centro earthquake.

In this section, a brief discussion will be presented dealing with maintenance issues of the stone-masonry bridges that were examined in this chapter. This study focused on the dynamic and seismic response of this type of bridges. However, it was shown by past experience that structural damage can also result from other types of actions such as flooding or traffic when such bridges are used not only for light pedestrian use. Because almost all the stone-masonry bridges in Greece have been built mostly for relatively light live load levels resulting from the crossing of pedestrians or animal flocks, their structural vulnerability due to traffic conditions is not an issue. Instead, flooding of the narrow gorge currents that these bridges cross (**Figure 49a**) is one of the main structural damage causes, as demonstrated from the Plaka Bridge (see **Figure 50a** and **b**). Apart from the hydrodynamic loads that a stone-masonry bridge is subjected to from a flooded current, one of the main sources of distress that may lead to partial or total collapse is the deformability of the foundation. The deformability of the foundation and the potential for subsequent collapse does include not only wash-out effects from a sudden flooded current but also the cumulative deformability of the foundation in a wider time

**Figure 49.** (a) Almost total flooding of a stone masonry bridge and (b) tilting of a mid-pier and partial collapse of the Diava-Kalampaka reinforced concrete bridge in Thessaly, Greece (16th January, 2016).

window as was demonstrated by a recent flooding of Pineios river that caused the tilting of a mid-pier and the partial collapse of the Diava-Kalampaka-reinforced concrete bridge in Thessaly, Greece (16 January 2016, **Figure 49b**).

**Figure 50.** (a) View of the Plaka Bridge after the collapse from the West bank. Note the total destruction of the mid-pier (see also **Figure 7d**). (b) Close-up of the total destruction of the mid-pier of Plaka Bridge (see also **Figure 7d**).

Thus, foundation maintenance seems to be of the utmost importance. The flooding of Arachthos river, which caused the collapse of Plaka Bridge on 31 January 2015, was of considerable proportions. It is of interest to observe the conditions of the mid-pier of Plaka Bridge after the collapse (**Figure 50a** and **b**). As can be seen, the foundation of this pier is almost non-existent being covered by the remains of the East part of central arch and of part of the adjacent arch and mid-pier. Thus, it is evident that this mid-pier was highly distressed leading to this mode of collapse.

Another maintenance issue of considerable importance is the integrity of the stone masonry in parts of the bridge apart from the foundation. It was already discussed in Section 6, when comparing numerically predicted with measured eigen-frequency values, that evidence of washed-out mortar joints was present mainly in Kontodimou, Tsipianis and Kokorou Bridges. At the time of *in situ* measurements (October to December 2015), maintenance works took place in Konitsa Bridge focusing on the removal of vegetation and re-pointing of the mortar joints. The effectiveness of these operations must be validated through laboratory testing regarding the compatibility and durability of the materials employed. The presence of metal ties and their structural function was underlined in Section 3. However, inspection of these metal ties in the stone-masonry bridges of the present study as well as other stone-masonry bridges not reported here casts doubts on their effectiveness due to lack of maintenance for a long time.

In some cases, these stone-masonry bridges suffered structural damage from human activity. Plaka Bridge is one such example as can be seen in **Figure 51a**. The red arrow in this figure points to the structural damage suffered by the central arch due to an explosion during World War II. The damaged part was retrofitted in a way that is not known in detail to the authors. This retrofitting is visible in detail in **Figure 51b** where one can distinguish the difference in the texture of the old stone masonry from the retrofitted part of the secondary arch in this location indicated by the red circle.

window as was demonstrated by a recent flooding of Pineios river that caused the tilting of a mid-pier and the partial collapse of the Diava-Kalampaka-reinforced concrete bridge in

**Figure 50.** (a) View of the Plaka Bridge after the collapse from the West bank. Note the total destruction of the mid-pier

Thus, foundation maintenance seems to be of the utmost importance. The flooding of Arachthos river, which caused the collapse of Plaka Bridge on 31 January 2015, was of considerable proportions. It is of interest to observe the conditions of the mid-pier of Plaka Bridge after the collapse (**Figure 50a** and **b**). As can be seen, the foundation of this pier is almost non-existent being covered by the remains of the East part of central arch and of part of the adjacent arch and mid-pier. Thus, it is evident that this mid-pier was highly distressed leading to this mode

Another maintenance issue of considerable importance is the integrity of the stone masonry in parts of the bridge apart from the foundation. It was already discussed in Section 6, when comparing numerically predicted with measured eigen-frequency values, that evidence of washed-out mortar joints was present mainly in Kontodimou, Tsipianis and Kokorou Bridges. At the time of *in situ* measurements (October to December 2015), maintenance works took place in Konitsa Bridge focusing on the removal of vegetation and re-pointing of the mortar joints. The effectiveness of these operations must be validated through laboratory testing regarding the compatibility and durability of the materials employed. The presence of metal ties and their structural function was underlined in Section 3. However, inspection of these metal ties in the stone-masonry bridges of the present study as well as other stone-masonry bridges not reported here casts doubts on their effectiveness due to lack of maintenance for a long time.

In some cases, these stone-masonry bridges suffered structural damage from human activity. Plaka Bridge is one such example as can be seen in **Figure 51a**. The red arrow in this figure points to the structural damage suffered by the central arch due to an explosion during World War II. The damaged part was retrofitted in a way that is not known in detail to the authors. This retrofitting is visible in detail in **Figure 51b** where one can distinguish the difference in the texture of the old stone masonry from the retrofitted part of the secondary arch in this

(see also **Figure 7d**). (b) Close-up of the total destruction of the mid-pier of Plaka Bridge (see also **Figure 7d**).

Thessaly, Greece (16 January 2016, **Figure 49b**).

122 Structural Bridge Engineering

of collapse.

location indicated by the red circle.

**Figure 51.** (a) Structural damage at the East part of the central arch of Plaka Bridge due to an explosion. (b) Detail of the retrofitted part of the secondary arch of the Plaka Bridge sometime before its collapse from flooding.

This is also visible in **Figure 52a** where the scaffolding used for additional maintenance works is also visible. However, these works did not prove sufficient to prevent the collapse of this bridge from the severe flooding. It is of great research interest to be able to apply the methodology of *in situ* investigation presented in Section 4 of this chapter together with a long-term monitoring and maintenance programme as means of safeguarding the structural integrity of these precious cultural heritage structures.

**Figure 52.** (a) Maintenance works at Plaka Bridge sometime before its collapse from flooding and (b) stone-masonry bridge at Dasilio-Grevena, Greece after being retrofitted.

In the brief space of this section, the principles that govern a major retrofitting of such bridges must also be underlined. This is very important not only for the collapsed Plaka Bridge and the plans for its reconstruction but for numerous other bridge structures that have suffered serious structural damage or partial collapse. **Figure 52b** depicts a stone-masonry bridge in North-Western Macedonia, Greece, which underwent major reconstruction. It is worth mentioning that the regions of North-Western Macedonia and Ipiros in Greece are the home of stone masons who have been active worldwide. Due to their initiative specific stonemasonry workshops have been established recently in this region in an effort to keep this type of traditional construction as well as its maintenance alive.
