PSI - Issue 84

Valentina Picciano et al. / Procedia Structural Integrity 84 (2026) 922–930

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debonding, which prevents full exploitation of the high tensile strength of the composite material. As a result, FRP based solutions could not be designed to provide the same flexural enhancement level as the other strengthening strategies, although they introduce negligible additional self-weight. Based on the latter, a first quantitative comparison among the considered strengthening techniques can be carried out in terms of structural efficiency. To this aim, the performance improvement is evaluated by accounting for the net increase in flexural capacity, i.e., by excluding the contribution of the additional permanent load introduced by the intervention. This allows the comparison of techniques not only in terms of absolute strength gain, but also in terms of how effectively this gain is achieved with respect to the added weight. A synthetic efficiency indicator (  ) is therefore introduced to express the ratio between the net increase in flexural capacity and the total strength enhancement provided by each intervention. This index enables a direct and intuitive comparison among the different strategies. The results of this comparison are summarized and graphically represented in Fig. 2. As can be observed, external post-tensioning emerges as the most efficient solution from a structural standpoint, with an efficiency index of 98.8%. Steel jacketing follows with a value of 96.2%, while reinforced concrete jacketing exhibits a significantly lower efficiency (86.4%), mainly due to the substantial increase in self-weight associated with this technique. FRP-based strengthening solutions show a markedly different behavior. Although composite materials are characterized by high tensile strength and low weight, the achievable flexural capacity increase remains limited ( ΔM ≤ 7.5%). This is mainly due to bond-related failure mechanisms, which prevent the full exploitation of the material strength.

Fig. 2. Comparison of the structural efficiency of the analyzed strengthening techniques (*FRP results refer to the achieved capacity increase).

To complement the structural efficiency assessment, a comparative cost analysis was carried out for the considered strengthening techniques. The estimation was based on the retrofit configurations defined previously, adopting simplified and consistent assumptions. Cost items related to preliminary and common operations, such as local concrete removal, reinforcement passivation, and minor surface restoration, were excluded from the computation, as they are generally required for any intervention and would not affect the relative comparison. Similarly, costs associated with access systems, scaffolding, and auxiliary equipment were assumed to be equivalent for all techniques. The cost evaluation was performed using the official unit prices provided by the Italian road infrastructure authority (ANAS 2024), while material quantities were derived from the design configurations or estimated based on standard construction practice. To ensure comparability, costs were normalized with respect to the beam length, and a synthetic cost indicator was introduced to relate the total expense to the net structural performance gain (as percentage) achieved by each intervention. The results of this analysis are summarized in Fig. 3. As can be observed, external post-tensioning is not only the most efficient solution from a structural standpoint, but also the most cost-effective one. This technique achieves the desired flexural capacity increase with significantly lower material quantities and reduced construction complexity, resulting in a considerably lower cost per unit of performance gain. Steel and reinforced concrete jacketing exhibit comparable cost levels, with reinforced concrete jacketing being slightly more economical.