###### Abstract  
According to modern structural codes, a design is considered to be adequate if the limit states are not exceeded. For the ultimate limit state, the design value of action effect \(\mathrm{E_{d}}\) is required to be less or equal than the design value of ultimate resistance \(\mathrm{R_{d}}\). This ensures, according to the Eurocode, a sufficiently low probability of failure expressed as the target reliability index \(\beta\). Consequently, the distributions of action effect and of resistance need to satisfy the following conditions: \(P(E>E_{d})\leq\Phi(+\alpha_{E}B)\) and \(P(R\leq\mathrm{R_{d}})\leq\Phi(-\alpha_{R}\beta)\), where \(\alpha_{\mathrm{E}}\) and \(\alpha_{\mathrm{R}}\), with \(|\,\alpha\,|\leq 1\), are the values of the FORM sensitivity factors. The values of the sensitivity factors \(\alpha_{\mathrm{E}}\) and \(\alpha_{\mathrm{R}}\) are suggested, according to EN1990, as \(-0.7\) and \(0.8\), respectively; for the accompanying actions, the sensitivity factor is recommended as \(0.28\). In this paper, the dependence of the sensitivity factors for traffic live load, dead load, and resistance on the ratio of traffic load to dead load is studied (which is directly proportional to the maximum span of the bridge). Significantly different sensitivity factors for resistance, dead load, and traffic load, other than proposed by the Eurocode, has been calculated for typical ratio of traffic to dead load. It further showed that, if it is assumed that \(\mathrm{E_{d}}=\mathrm{R_{d}}\) and the Eurocode partial safety factors are used, a different design point than the starting point, i.e., \(\mathrm{E_{d}}=\mathrm{R_{d}}\), is obtained. sensitivity factor; partial factor calibration; traffic load; existing bridges assessment Article Dependence of Sensitivity Factors on Ratio of Traffic Load to Dead Load  
[PERSON], [PERSON], R.  
Sensitivity factors may be interpreted as factors giving the relative importance of the individual random variable for the reliability index \(\beta\), i.e., the probability of failure, as shown graphically in Figure 1. The sensitivity factors \(\alpha_{\rm E}\) and \(\alpha_{\rm R}\) may be taken according to EN1990 as \(-0.7\) and \(0.8\), respectively. For the accompanying actions, the design values may be defined by P(E > Ed) = \(\Phi\)(\(-0.4\)\(\times\)\(0.7\)\(\times\)\(\beta\)) = \(\Phi\)(\(-0.28\)\(\beta\)). The condition for these expressions are that \(0.16<\sigma_{E}/\sigma_{R}<7.16\), where \(\sigma_{\rm E}\) and \(\sigma_{\rm R}\) are standard deviations for the action effect and for resistance, respectively. Otherwise, \(\alpha=\pm 1.0\) should be used for the variable with the larger standard deviation, and \(\alpha=\pm 0.4\) for the variable with the smaller standard deviation. These values of the sensitivity factors are based on the study where the deviation from the target reliability index for different values of the ratio between the standard deviation of the random variable R and E was minimized [3]. The fib Bulletin 80 [4] proposes two methodologies devoted to the redefinition of the partial safety factors for the assessment of existing structures: the design value method (DVM) and the adjusted partial factor method (APFM). The DVM allows for recalculation of the partial safety factors for both resistances and actions by means of consistent probabilistic models derived by the prior knowledge, test results, and observations related to the existing structure under investigation. The APFM, which can be considered the simpler approach, allows for the update of the partial safety factors defined by the Eurocode for new structures by means of \"adjustment coefficients\" accounting for the prior knowledge, test results, and observations related to the existing structure.