BIBLIOGRAPHIC REVIEW OF ITALIAN REGULATIONS FROM 1900 TO THE PRESENT FOR THE SIMULATED DESIGN OF ITALIAN RAILWAY BRIDGES Antonella Di Meo1, Barbara Borzi2, Davide Bellotti2, and Francesco Bruno2 1 European Centre for Training and Research in Earthquake Engineering (Eucentre) Via Adolfo Ferrata, 1, 27100, Pavia (Italy) e-mail: antonella.dimeo@eucentre.it 2 European Centre for Training and Research in Earthquake Engineering (Eucentre) Via Adolfo Ferrata, 1, 27100, Pavia (Italy) {barbara.borzi, davide.bellotti, francesco bruno}@ eucentre.it Abstract The many catastrophic earthquakes that occurred in Italy in the last fourty years underline how Italy is one of the European countries at the highest seismic risk. For this reason, the vulnerability of infrastructures needs to be investigated. This paper considers the railway network as a case study with a focus on railway bridges, which are neuralgic nodes of the whole system. The most common types of railway bridges in Italy are masonry arch bridges and girder bridges with either a continuous deck or a simply supported deck. Here, we specif- ically analyze railway girder bridges. Eucentre evaluates the seismic vulnerability of railway bridges through the definition of fragility curves. Fragility curves result from analytical procedures that determine the seismic behaviour of structures according to the structural typology as well as the level of knowledge of the bridge. One step of these procedures is the simulated design, which aims at reducing the number of variables in the process and requires the knowledge of the regulatory limits used at the time of the design. This paper presents those regulatory limits that concern: (i) loads, (ii) materials resistance, (iii) longitudinal and transversal reinforcement percentages for reinforced concrete bridges, and (iv) bearings. These limits derive from a detailed biblio- graphic study on Italian regulations, concerning the design of railway bridges from the be- ginning of 1900 to the present. Keywords: Railway Bridges, Italian Regulation, Simulated Design, Seismic Vulnerability. 4598 COMPDYN 2019 7th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering M. Papadrakakis, M. Fragiadakis (eds.) Crete, Greece, 24–26 June 2019 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2019) 4598-4614 ISSN:2623-3347 © 2019 The Authors. Published by Eccomas Proceedia. Peer-review under responsibility of the organizing committee of COMPDYN 2019. doi: 10.7712/120119.7253.18862 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno 1 INTRODUCTION The Italian railway network is made up of about 17000 km of rail lines that are in opera- tion and are largely developed in medium-to-high seismic hazard zones. Important elements of this network are viaducts. The most common types of railway bridges in Italy are masonry arch bridges and girder bridges with either a continuous deck or simply supported deck. In this paper, only the railway girder bridges are analyzed, a brief description of which is also given in relation to the deck material. The seismic vulnerability of railway bridges is generally assessed through fragility curves. Fragility curves can be obtained through different methods, such as analytical methods that involve the mechanical modeling of the structure. For the seismic behaviour of the modeled structure to be plausible, the characteristics of materials, the amount of reinforcement, and the types of bearings used in the modeling need to be as close as possible to the actual conditions of the bridge. This information is included in the project documents which are usually not available. To solve this problem, the simulated design of the structure is carried out using the limits imposed by the regulations in force at the time of design. To this end, this paper provides a brief bibliographic review of the regulations used for the construction of reinforced concrete railway bridges from the beginning of the last century to the present day. The first Italian regulation available on the design of reinforced concrete railway bridges dates back to 1995. For this reason, the provisions on the reinforcement of piers as well as on the mechanical characteristics of materials derive from the regulations is- sued in Italy starting from 1907 concerning the construction of public reinforced concrete structures. For mobile loads, instead, specific technical standards have been considered start- ing from 1946. The definition of the permanent load depends on the composition of the superstructure. For this purpose, this paper also provides the weights of the railway track and ballast, as well as the weight of noise barriers suggested by the latest technical specifications issued by the Ital- ian State Railways ([1], [2], [3]). Finally, this paper gives a brief bibliographic review of the standards on the types of bear- ings for railway girder bridges from 1972 onwards. It is very important to identify the geo- metrical and mechanical characteristics of these devices so that their actual function can be taken into account during their simulated design. A wrong modeling of bearings could affect the actual seismic response of a bridge because it changes the way in which mechanisms of the pier-bearing system are activated. 2 RAILWAY GIRDER BRIDGES One of a widely used bridge typology in the Italian railway network is represented by gird- er bridges. The deck can consist of reinforced concrete, prestressed reinforced concrete, or steel, and generally lies on unreinforced concrete, reinforced concrete, or masonry piers. The deck can be simply supported or continuous, thus giving rise to an isostatic or hyperstatic stat- ic scheme, respectively. Between the deck and the vertical structure of the bridge are the bear- ings, the choice of which depends mainly on the type of deck and the type of constraint to be obtained. In case of a reinforced concrete deck, the method of construction depends mainly on the length of the individual spans as well as on the total length of the bridge. Specifically, the deck can be made of: (i) a slab, (ii) steel girders embedded in concrete, and (iii) reinforced concrete plate girder. The bridge with slab deck is the simplest system used in rail transport, but only when the spans do not exceed 4 m. On the contrary, the deck with steel girders em- 4599 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno bedded in concrete or reinforced concrete plate girder is used when, for orographic reasons, the deck cannot be very thick. In particular, the deck with steel girders embedded in concrete is no longer than either 13 m, in the case of “double T” beams, or 20 m, in the case of “double T” beams with wide wings. In presence of a deck with reinforced concrete plate girder, in- stead, the girders also have the function of parapet and can reach heights of also 3.5 m. The deck is continuous and supports the railway superstructure. In addition to reinforced concrete, the deck can be realized with prestressed reinforced concrete beams. This deck can reach a length that ranges 35 m and 50 m and is generally made of isolated or box beams. When the beam has a box cross-section, the common practice provides for the use of a box for each track. In this case, the beams are connected among each other with cross-beams (which are prestressed, too) to guarantee the beams cooperation in the usual load conditions (e.g. the passage of a train) so that fatigue phenomena can be reduced. Nowadays, the prestressed reinforced concrete deck is really common on both ordinary and high-speed railway lines. Another type of deck is the steel deck, which has been widely used in the past; nowadays, however, it is mainly used for long span bridges with reduced height or to replace pre-existing steel girders. Because of the high cost of construction and maintenance, steel decks have mostly been replaced by either the prestressed reinforced concrete decks for medium-to-long span bridges, or reinforced concrete and mixed structure decks for bridges with shorter spans. The most common railway steel bridges are made of straight girders lying on masonry or rein- forced concrete piers. In the case of bridges with more than one span, however, it is preferable to create non-continuous decks on which the track can be either direct lying or ballasted. De- pending on the length of the deck, the direct-laying girders can be twin-girders (for spans be- tween 10-25 m), plate girders (for spans between 30-40 m), or truss girders (for spans between 35-100 m). For what concerns bridges with railway tracks lying on the ballast, they generally have a deck with steel-concrete composite girders. In this case, the beams can be “double T” or box section collaborating with the concrete slab and reach a length of about 20- 25 m. To guarantee the interaction between all the girders of the deck, cross-beams are also used, especially in the presence of live loads. 3 ITALIAN REGULATIONS FROM 1900 TO NOWADAYS FOR RAILWAY GIRDER BRIDGES 3.1 Resistance of Materials The first recommendations about the construction of reinforced concrete structures were issued in Italy with the Royal Decree 10/01/1907 [4]. This decree provided the first indica- tions about the maximum strength to be considered in the structural calculation for both con- crete and reinforcement. In particular, this standard stated that the compressive strength of concrete at 28 days of hardening σr,28 must not be less than 150 kg/cm2, the fifth part of which corresponds to the simple compressive safety load of the concrete to be used in the calculation. Concerning the reinforcement, the regulation allowed the use of smooth steel rebars with a tensile strength between 36 kg/mm2 and 45 kg/mm2. The safety tensile and shear loads, in- stead, should not exceed 1000 kg/cm2 and 800 kg/cm2, respectively. For the reinforcement, the decree introduced a further limitation, namely the quality coefficient, which is obtained by multiplying the unit failure load per mm2 by the percentage elongation. This coefficient, which should not exceed 900, was then replaced by the percentage of elongation at maximum tensile strength of the reinforcement in the Royal Decree issued on 4/09/1927 [5]. With the exception of this introduction, the Royal Decree 4/09/1927 [5] has not made substantial changes compared to what was already established by the previous decree [4]. In fact, the de- 4600 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno cree only reduced and slightly increased the values of the safety concrete load (30 kg/m2 and 40 kg/m2 for 2nd and 1st quality concretes) as well as the tensile and shear steel ones (1200 kg/cm2 and 960 kg/cm2). As a result, the tensile strength of the steel changed slightly, i.e. 3800-5000 kg/cm2, corresponding to a minimum elongation of 27% and 21%, respectively. With the Royal Decree 23/05/1932 [6], the classification of concretes had been improved and divided into Portland, blast furnace, pozzolanic, and aluminous. Portland, blast furnace, and pozzolanic concretes could be of normal or high strength (see Table 1). The mechanical characteristics of steel, instead, did not change compared to what was already indicated in the Royal Decree 4/09/1927 [5]. Mechanical characteristics of concrete Portland, blast furnace, pozzolanic concrete Aluminous concrete Normal strength High strength Crushing strength [kg/cm2] 450 600 650 Compressive safety load [kg/cm2] 40*-50** 50 65 Maximum tangential strength with- out reinforcement [kg/cm2] 2 4 4 Maximum tangential strength with reinforcement [kg/cm2] 14 16 16 *for structures under simple pressure; **for bent structures with a thickness not less than 10 cm. Table 1: Mechanical characteristics of portland, blast furnace, pozzolanic, and aluminous concretes in the Royal Decree 23/05/1932 [6]. The Circular 17/05/1937 [7] introduced the use of medium carbon steel, only in absence of homogeneous steel. In terms of mechanical characteristics, the medium carbon steel had an ultimate tensile strength between 5000 kg/cm2 and 6500 kg/cm2 to which percentages of elon- gation corresponded to 21% and 14%, respectively. The safety load of the steel increased from 1200 kg/cm2 to 1600 kg/cm2. In 1939 a new Royal Decree [8] was issued to regulate the construction of structures made of unreinforced or reinforced concrete. In this decree, the compressive strength of concrete at 28 days of hardening σr,28 had to be at least three times the safety load σc,a adopted in the structural calculations, but never less than 120 kg/cm2 and 160 kg/cm2 for normal-strength concrete and high-strength or aluminous concrete, respectively. Regarding the reinforcement, the Royal Decree 16/11/1939 [8] introduced high carbon steel, which allowed to adopt small- er rebar sizes due to its high specific resistance [9]. Table 2 reports the mechanical properties of the three types of steel permitted by the Royal Decree 16/11/1939 [8]. Mechanical characteristics of steel Mild Steel Medium carbon steel High carbon steel Yield characteristic strength [kg/cm2] ≥2300 ≥2700 ≥3100 Ultimate characteristic strength [kg/cm2] 4200-5000 5000-6000 6000-7000 Elongation [%] ≥20 ≥16 ≥14 Safety load [kg/cm2] ≤1400 ≤2000 ≤2000 Table 2: Mechanical characteristics of steels in the Royal Decree 16/11/1939 [8]. The Royal Decree 16/11/1939 [8] has remained in force until the first years of 1970s as a consequence of a regulatory gap due to the Second World War and the following period of 4601 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno reconstruction. Between 1939 and the early 1970s, however, a series of circulars have been issued, among which it is necessary to mention the Circular 23/05/1957 [10]. This circular not only introduced a new denomination for smooth steel rebars, i.e. AQ42, AQ50 and AQ60, equivalent respectively to the mild, medium carbon, and high carbon steel of Table 2, but also introduced first indications on ribbed steel rebars [9]. The ribbed steel rebars were allowed in special cases, such as shaped or bent rebars, and with a minimum elongation percentage of 12%. A substantial change with respect to the previous regulations occurred with the Ministerial Decree 30/05/1972 [11] which has laid the foundations of modern legislation. It introduced a classification of ribbed steel rebars as well as a calculation method at the limit states, which replaced the permissible stresses approach. This change defined the transition from a deter- ministic to a statistical calculation system due to the introduction of the characteristic value. As a consequence, the yield strength and the ultimate strength were not intended anymore as an average value but as the strength that had only a 5% probability of being lowered by the effective resistance [9]. The Ministerial Decree of 30/05/1972 [11] distinguished six classes of concrete by a number that expressed the characteristic cubic resistance at 28 days of harden- ing R'bk, from which it was possible to obtain the mechanical characteristics of the concrete (e.g. compressive strength, tensile strength, etc.). For what concerns the reinforcement, smooth steels were divided in only two classes (i.e. Fe B 22 and Fe B 32), and the ribbed steel rebars into three classes (i.e. A 38, A 41, and Fe B 44) (see Table 3). Mechanical characteristics of steel Smooth steel rebars Ribbed steel rebars Fe B 22 Fe B 32 A 38 A 41 Fe B 44 Yield characteristic strength [kg/cm2] ≥ 2200 ≥ 3200 ≥ 3800 ≥ 4100 ≥ 4400 Ultimate characteristic strength [kg/cm2] ≥ 3400 ≥ 5000 ≥ 4600 ≥ 5000 ≥ 5500 Elongation [%] ≥ 24 ≥ 23 ≥ 14 ≥ 14 ≥ 12 Safety load [kg/cm2] 1200 1600 2200 2400 2600 Table 3: Mechanical characteristics of smooth steel rebars and ribbed steel rebars in the Ministerial Decree of 30/05/1972 [11]. After 1972, other decrees were issued about the construction of reinforced concrete struc- tures, but they have not considerably changed the provisions of the Ministerial Decree 30/05/1972 [11] in terms of mechanical characteristic of materials. This is evident in Table 4 and Table 5, which report the mechanical characteristics of the rebars defined in the latest standards on the construction of railway bridges, issued by Italian State Railways ([1], [2], [3]). The only significant difference between the Circular n. I/SC/PS-OW2298 1997 [1] and the newest Technical Specifications by Italian State Railways ([2], [3]) is the mechanical characteristics of ribbed steel rebars (see Table 5). As stated in the Italian Seismic Codes (NTC08) [12], the use of smooth steel rebars is definitely prohibited. Concerning concrete properties, no substantial changes were made. 4602 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno Mechanical characteristics of steel Smooth steel rebars Ribbed steel rebars Fe B 22k Fe B 32k Fe B 38k Fe B 44k Yield characteristic strength [kg/cm2] ≥ 2150 ≥ 3150 ≥ 3750 ≥ 4300 Ultimate characteristic strength [kg/cm2] ≥ 3350 ≥ 4900 ≥ 4500 ≥ 5400 Elongation [%] ≥ 24 ≥ 23 ≥ 14 ≥ 12 Table 4: Mechanical characteristics of smooth steel rebars and ribbed steel rebars in the Circular n. I/SC/PS- OW2298 and following update of 1997 [1]. Mechanical characteristics of steel B450C Yield characteristic strength [kg/cm2] ≥ 4500 Ultimate characteristic strength [kg/cm2] ≥ 5400 Elongation [%] ≥ 7.5 Table 5: Mechanical characteristics of ribbed steel rebars in the newest technical specifications by Italian State Railways ([2], [3]). 3.2 Definition of loads 3.2.1 Permanent loads The permanent loads are obtained from the structural and non-structural loads, to which the hydraulic and lateral earth pressures are added too, if existing. The permanent structural loads are evaluated on the basis of the geometric characteristics of the elements constituting the deck of the bridge (i.e. girders, cross-beams, and slab) and the specific weights of the materials with which they are made. The latter are regulated by the codes in force at the time of the structure design. The non-structural load, instead, is obtained by adding the weight of all non-structural el- ements composing the superstructure, that are mainly: (i) the railway track, (ii) the ballast, (iii) the waterproofing, and (iv) the noise barriers. A railway track is defined as the totality of rails, sleepers, and fasteners. The first rails were entirely made of cast iron, were very short, and mounted on large stone blocks drowned in the ground. Due to the fragility of cast iron, it was later replaced by iron, which is, however, subjected to wear. The solution to the problem of wear was the “double headed rail”, which was mounted through hardwood wedges into special fixing plates, fixed in turn on wooden sleepers. When the upper table was worn out, the rail was inverted so that the lower table was ready to be used. As this process was complex and expensive, other solu- tions were developed, such as the “Vignoles rail” (named by the engineer who invented it), which has a “double-T” profile with a wider lower table than the upper one. Advances in ma- terial science led to the replacement of iron with steel: steel performs better than iron and de- forms less at high speeds. The intended use of the tracks defines the type of steel used for the rails, their dimensions and, consequently, the weight and maximum permissible speed of the vehicles. The higher the linear weight of the rail, the higher are its performances. Initially, the rails had a weight of 18-25 kg/m or 27 kg/m. Later on, rails with a weight of 36 kg/m and 46- 48 kg/m became very common for secondary and main railways, respectively. Since the 1960s, during the maintenance of existing railway systems, Italian State Rail- ways replaced the old rails with “Vignoles” types UIC 50 and UIC 60. In Italy, the code that describes the “Vignoles” type rails is UNI-3134 [13] which doesn't differ much from the Eu- 4603 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno ropean and UIC (i.e. Union Internationale des Chemins de fer) regulations. Table 6 shows the weight of rails in kg/ml according to UNI-3141 [13]. Type Weight [kg/m] H [mm] F [mm] B [mm] A [mm] 21 21.373 100 50 80 10 27 27.350 120 50 95 11 30 30.152 125 56 100 12 36 36.188 130 60 100 14 46 46.786 145 63.5/67.2 135 14 50 49.850 148 65.2/70 135 14 60 60.34 172 70.6/74.3 150 16.5 Table 6: Weight and geometrical properties of rails in kg/m according to UNI-3141 [13]. The sleepers, instead, can be made of wood or prestressed reinforced concrete. Wooden sleepers are the oldest and still widespread. For reasons of cost, of supply as well as of a reduced service life due to adverse weather conditions, in the past wooden sleepers were replaced by iron ones. Nowadays, especially on high-speed rails, prestressed concrete mono-block or twin-block sleepers are used. The twin-block sleepers differ from the mono- block types because they consist of two parallelepiped prestressed concrete elements connect- ed to each other by a steel bar. Table 7 shows the geometric characteristics and the sleeper’s weight in kilogram. To calcu- late the weight per meter, it is necessary to refer to the module, i.e. the number of sleepers that are in 6 m of track length. The module depends on the class of the railway line, and conse- quently on the maximum load and speed of the train, and can be: • Module 6/10, i.e. 10 sleepers in 6 m (used for tracks belonging to the main rail network suitable for the highest speeds, for 18 t/axle in case of isolated axles, and for more than 18 t in case of locomotive axles); • Module 6/9, i.e. 9 sleepers in 6 m (used for complementary rail network as well as for crossing or priority rails suitable for lower speeds, for 18 t/axis in case of isolated axles, and for more than 18 t in case of locomotive axles); and • Module 6/8, i.e. 8 sleepers in 6 m (used for tracks belonging to the secondary rail network as well as for all other rails suitable for even lower speeds and 16 t/axis in case of isolated axles). To connect the sleepers to the rails, and often to ensure electrical insulation, the used fas- teners can be of different types; their weight has little impact on the non-structural load. Type of sleeper Length [mm] Depth [mm] Thickness [mm] Weight [kg] Wood 2600 260 160 80 – 100 Prestressed concrete mono-block 2300 - 2600 300 180 – 230 250 – 370 Prestressed concrete twin-block 2300 300 220 245 Table 7: Geometric characteristic of the sleepers. The railway tracks generally lay on a layer of ballast; the latter can be replaced by a con- crete plate in very special cases, such as viaducts with an isostatic structure and length span 4604 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno not exceeding 30 m. The ballast is a layer of crushed stone with a thickness that can be about 50 cm or 35 cm, depending on whether the importance of the rail network is primary or sec- ondary. The stone material has an internal friction angle of not less than 45° and an apparent volumetric mass of not less than 1.5 t/m3. Between the deck and the ballast exists a waterproofing layer consisting of two sheaths, one at the top and one at the bottom, and a protective layer of bituminous conglomerate about 5 cm thick. The membranes at the top and the bottom of the waterproofing layer have a thick- ness of about 5 mm and 3 mm, respectively, and a weight of 4 kg/m2 and 3-3.5 kg/m2, respec- tively. The bituminous conglomerate generally weighs 80-90 kg/cm2. Finally, the superstructure is also composed of noise barriers, the weight of which is usual- ly taken from the manufacturer’s data sheets. Table 8 shows the weight and height to be considered for the design of the noise barriers provided by: (i) the Circular n. I/SC/PS-OW2298 1997 [1], (ii) the Technical Specification “RFI DTC INC PO SP IFS 001 A” 2011 [2], (iii) and the Manual for the Design of Civil Structures “RFI DTC SI PS MA IFS 001 A” 2016 [3]. Regulation Weight [kN/m2] Height from the slab floor [m] Circular 13/01/1997 [1] 2,0 4,0 Technical Specification “RFI-DTC-INC-PO-SP- IFS-001-A” 2011 [2] 4,0 4,0 Manual for the design of civil Structures “RFI DTC SI PS MA IFS 001 A 2016 [3] 4,0 4,0 Table 8: Prescriptions for noise barriers ([1], [2], [3]). In the case of a superstructure consisting of ballast, railway track, and waterproofing (in- cluding the bituminous conglomerate), the non-structural load can be simply calculated by considering a total volume weight of 18 kN/m3. This volume weight is applied over the entire average width between the paraballast walls, for an average height between the top rail and the extrados of the deck equal to 0.80 m. For bridges in curved railway sections, , the weight of the ballast used to create the superelevation must be added to the conventional weight indi- cated above, which is evaluated with its actual geometric distribution and with a volume weight of 20 kN/m3 ([1], [2], [3]). 3.2.2 Train Live Loads The simulated design of railway bridges requires an estimate of the train live loads used in the planning step according to the year of structure design. For reinforced concrete bridges, the first regulation on this topic was issued in 1946, when Circular 30/10/1946 [14] introduced a formula for the evaluation of a dynamic increase coef- ficient φ to be used for reinforced concrete bridges: 4P/S1 0.6 0.2L1 0.4 + + + =ϕ , (1) in which L is the theoretical load capacity of the beam, P the overload, and S the perma- nent load. For the concrete structures design before the Circular n. I/SC/PS-OW2298 1997 [1], the increase in load due to the passage of trains was carried out by increasing the values of 4605 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno overloading by 25%. This criterion derived from some regulations concerning the construc- tion of concrete structures that were issued before 1945. From 1945 until the following year, instead, the design of reinforced concrete bridges was carried out by using the dynamic increase coefficient φ defined in the Circular 15/07/1945 [15] for steel bridges: its value depended on both the design speed V and the theoretical capacity L of the structural element to be designed. Specifically, if rail joints were absent or only welded, the dynamic increase coefficient φ was assumed to be maximally of 40% to be associated to the elements of limited theoretical capacity L. This value was subsequently increased to 50% as well as the maximum design speed Vmax that became equal to 100 km/h. As a consequence, the dynamic increase coefficient φ never exceeded 50%. Concerning the train live loads, Cir- cular 15/07/1945 [15] defined two types of load in relation to the presumed railway traffic, i.e. “Type A” and “Type B” (see Figure 1). Alternatively, for the calculation of longitudinal ties, cross-beams, and structural elements with a low theoretical load capacity, the standard al- lowed the use of an isolated axle of 30 t and 25 t, instead of the train live loads “Type A” and “Type B”, respectively. Before the Circular 15/07/1945 [15], other regulations defining the train live loads were is- sued in Italy, but we did not consider them here as they concerned exclusively iron and ma- sonry railway bridges, which were in the past much more common than the ones made of reinforced concrete. In Figure 2 we report only the train live loads used to design railway bridges before 1916, when the Italian State Railways was founded. (a) (b) Figure 1: (a) “Type A” and (b) “Type B” train live loads, used for the design of railway bridges according to Circular 15/07/1945 [15]. N° 2 Locomotives Limited number of vagons TYPE B N° 2 Locomotives Limited number of vagons TYPE A 4606 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno (a) (b) Figure 2: (a) “Category IV” and (b) “Category V” train live loads, used to design railway bridges before the standard issued in 1916. The provisions of the Circular 15/07/1945 [15] have remained valid until 1995, when the Circular n. I/SC/PS-OW2298 "Overloads for the calculation of railway bridges - Instructions for design, execution and testing" were issued, and then updated in 1997 [1]. This Circular incorporated the instructions from the Eurocodes and introduced two new models of train live load that replaced the previous ones. The new models of train live loads were: • for normal railway traffic “LM71”; • for heavy railway traffic “SW”, which was available in two different configurations “SW1” and “SW2”. The characteristic values attributed to the load models had to be multiplied by an adapta- tion coefficient α, which varied according to the category of the railway bridge to be designed (see Table 9). Bridges could belong to two different railway categories, i.e. “ Category A” and “Category B”. In particular, bridges in “Category A” applied to railways on which heaviest trains circulated or should be able to circulate; on the contrary, bridges in “Category B” ap- plied to the secondary railways of normal gauge, not included in “Category A”. Load model Adaption coefficient α Category A Category B LM71 1.1 0.83 SW/0 1.1 0.83 SW/2 1.0 0.83 Table 9: Adaptation coefficient α depending on the load model and the bridge category defined in Circular n. I/SC/PS-OW2298 " and its following update [1]. As it can be seen from Figure 3a, contrary to the provisions of the previous regulations, the train live load was represented by both axial and distributed loads. In particular, the load model for normal traffic “LM71” consisted of four axles Qvk of 250 kN, placed at a distance of 1.60 m from one another, and of a distributed load qvk of 80 kN/m in both directions, starting from 0.8 m from the end axles Qvk till an unlimited length. In addi- 4607 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno tion, for this load model an eccentricity of the load towards the track axis was contemplated, depending on the gauge s, to take into account the displacement of loads. The load model for the heavy traffic “SW” (see Figure 3b), instead, was characterized by two distinct configurations, as shown in Table 10. Finally, for some particular controls, the Circular introduced a special train live load called “Unloading Train”, represented by an uniformly distributed load equal to 12.5 kN/m. a) b) Figure 3: a) Load model for normal railway traffic “LM71” and b) Load model for heavy railway traffic “SW” defined in the Circular n. I/SC/PS-OW2298 and following update in 1997 [1]. Load model Qvk [kN/m] a [m] c [m] SW/0 133 15.0 5.3 SW/2 150 25.0 7.0 Table 10: Load model for heavy railway traffic “SW” defined in the Circular n. I/SC/PS-OW2298 and fol- lowing update in 1997 [1]. The Circular n. I/SC/PS-OW2298 1997 [1] further introduced two different dynamic in- crease coefficients φ in relation to the state of maintenance of the railway line which could be standard or reduced. These coefficients had to be applied to the theoretical load models “LM71” and “SW” in case of a static analysis, to take into account the movement effects and any imperfections of the rail, the wheels, and the suspension system. The Circular n. I/SC/PS- OW2298 1997 [1] also contemplated real dynamic increase coefficients φreal to be multiplied to load models representing a real train. Real train load models are used in particular condi- tions of analysis (or for the design of specific bridge typologies) and are made of concentrated loads, variously spaced, that schematize the succession of the axes of convoys actually or po- tentially circulating; each of them was characterized by a maximum speed and a certain over- all length [3]. Finally, the latest “RFI DTC INC PO SP IFS 001 A” 2011 [2] and “RFI DTC SI PS MA IFS 001 A” 2016 [3] assume the same load models defined in the Circular n. I/SC/PS- OW2298 1997 [1]. The only differences are: (i) the adaptation coefficient α, which herein de- pends only on the load model (see Table 11), (ii) the calculation of the real dynamic coeffi- cient φreal, and (iii) the value corresponding to the unloading train, which became 10.0 kN/m. UNLIMITED UNLIMITED 4608 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno Load model Adaption coefficient α LM71 1.1 SW/0 1.1 SW/2 1.0 Table 11: Adaptation coefficient α depending on the load model defined in “RFI DTC INC PO SP IFS 001 A” 2011 [2] and in “RFI DTC SI PS MA IFS 001 A” 2016 [3]. 3.3 Longitudinal and transverse reinforcement In the seismic assessment of existing reinforced concrete bridges through analytical meth- ods, the amount of longitudinal and transverse reinforcement in the piers needs to be known. This information is usually given in construction plans, but not often available. To fill this gap, the amount of the reinforcement can be derived from the appropriate code that was in use at the time of the structure design. Table 12 reports the minimum values of both longitudinal and transverse reinforcement de- fined from the Royal Decree 16th November 1939 [8] to the Ministerial Decree 4th 1992 [16]. The Royal Decree 10th January 1907 [4] is excluded since it does not contain any information on the reinforcement to be placed in the reinforce concrete structural vertical elements. In- stead, we deal separately with the Circular n. I/SC/PS-OW2298 1997 [1], the Technical Spec- ification “RFI DTC INC PO SP IFS 001 A” 2011 [2], and the Manual for the Design of Civil Structures “RFI DTC SI PS MA IFS 001 A” 2016 [3] because they are regulations issued di- rectly by Italian State Railways. In particular, for all viaducts built in territories seismically classified in 1st category (S=12, where S represents the seismicity level), 2nd category (S=9), 3rd category (S=6), the Circular n. I/SC/PS-OW2298 1997 [1] defined the minimum quantity of longitudinal reinforcement as 0.6%Aeff, where Aeff is the area of the effective concrete cross-section. This limit changed to 0.4%Aeff for all viaducts designed in the 4th seismic zone category (i.e. not classified zone), with the exception of the Sardinia region. In addition, the longitudinal rebars had not to be more than 300 mm apart. The diameter of the stirrups and transverse ligatures, instead, had not to be less than 8 mm and was obtained according to relationships that depended on the cross-section type of the pier, i.e. whether they were rectangular or circular, in both cases sol- id or hollow. Furthermore, in piers with a solid or hollow circular cross-section the use of spi- rals was not permitted anymore and were replaced by circular stirrups. To increase the level of ductility of the structure, the distance s between the stirrups had to be more than 10 times the minimum diameter of the vertical rebars. The Technical Specification “RFI DTC INC PO SP IFS 001 A” 2011 [2] and the Manual for the Design of Civil Structures “RFI DTC SI PS MA IFS 001 A” 2016 [3] resumed with the established values from the Circular n. I/SC/PS-OW2298 1997 [1]. Regardless of the seismic category for which the viaduct was designed, both Technical Specification and Manu- al for the Design of Civil Structures ([2], [3]) fix a minimum longitudinal reinforcement value of 0.6%Aeff. As established in the Circular n. I/SC/PS-OW2298 1997 [1], the longitudinal rebars should be connected by stirrups, which should have a diameter greater than 8 mm, but a pitch neither greater than 10 times the diameter of the longitudinal bars they connect nor 1/5 of the diameter of the section core inside them. In addition, piers with hollow section should have at least 6 ties per square meter connecting the longitudinal reinforcements. Finally, the limitations to define the diameter of pier stirrups provided by the Circular n. I/SC/PS- OW2298 1997 [1] were also present in the Technical Specification [2] and the Manual for the Design of Civil Structures [3]. The only difference was that such limitations only applied if the bridge design required the use of a structure factor q equal or less than 1.5. 4609 Antonella Di Meo, Barbara Borzi, Davide Bellotti, and Francesco Bruno Code Longitudinal reinforcement Transversal reinforcement R.M.D. 16/11/1939 [8] As≥0.8 % Ac (Ac ≤ 2000 cm2) As ≥0.5 % Ac (Ac ≥ 8000 cm2) 0.8%Ac