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presently the tallest and longest masonry bridge built in Portugal. Today, both bridges have electrified rail tracks and allow the circulation of trains with the maximum load authorized in the Portuguese rail network.

a) b)

c) d)

Figure 2.8 – Côa bridge: a) in 1948 (Reitor Pinto) and b) nowadays; Tâmega bridge: c) in 1947 (http://monumentosdesaparecidos.blogspot.com) and d) nowadays.

Overview on railway stone masonry bridges

a)

b)

c)

Figure 2.9 – Historical train load models: a) Italian code standard (issued in 1906); b) German code standard (issued in 1925); c) Portuguese code standard (issued in 1929).

Currently, according to the Eurocodes (CEN, 2003), the static loading scheme used in bridge structural analysis is represented by the load model LM71 proposed by UIC to simulate the envelope of several types of trains. The load configuration of the LM71 model is also used as a design load for railway bridges according to Eurocode 1 (EN1991-2, 2003) with the characteristic values shown in Figure 2.10-a for bridges on r2.10-ail tr2.10-acks with norm2.10-al tr2.10-affic. In r2.10-ailw2.10-ay lines with he2.10-avier or lighter tr2.10-affic th2.10-an the normal one, the characteristic values of LM71 loads are multiplied by a factor α. When multiplied by this factor, the loads are also called "classified vertical loads". The factor α ranges between 0.75 and 0.91 for rail tracks with lighter traffic and between 1.10 and 1.46 for the case of heavier rail traffic.

The load models SW/0 and SW/2 are also described in the standard EN 1991-2, constituting an alternative to the LM71 model. The load distribution is shown in Figure 2.10-b, and consists of two uniform loads arranged along with two bands.

a)

b)

Figure 2.10 – Load models in EN1991-2: a) LM 71; b) SW/0 and SW/2 (CEN, 2003).

As stated by De Santis and De Felice (2014), the traffic loads provided by current codes standard for bridge analysis and design are 67% higher than those envisioned by bridge builders in 1906. Because of the rapidly growing demand for railway passenger and goods transport, locomotives were permanently improved. In Portugal, from 1835 to 1931, the weight of locomotives expanded from 12 tons Le Belge steam locomotive with 4 ton/axle to 98 tons Henschel and Sohn steam locomotive with 18 ton/axle. This corresponds to an increase in uniform load from 2.5 to 7 tons per metre.

In addition to the locomotives’ weight, which were mainly driven by the first steam engines, the heavy goods railway transport has significantly changed. Nowadays, locomotives are much stronger compared to the old days, which yields not only higher starting tensile forces but also heavier railway wagons.

Presently, the axle loads of railway wagons exceed the axle loads of locomotives and show much higher deviations caused, for example, by overload or unbalanced load distribution.

An evaluation of the static loads acting in the Portuguese railway infrastructure is summarized in Table 2.3, where the maximum loads and axle loads for the most representative trains are presented. The axle load for passenger trains normally varies from 12 to 14 tons, and in the case of locomotives it varies from 20 to 22 tons; for freight wagons, the maximum value is 22.5 tons. The heaviest locomotive and the fastest train operating in the Portuguese railways are presented in Figure 2.11.

Table 2.3 – Total and axle loads for the most representative trains operating in Portuguese railway lines.

Vehicle Total load (ton) Axles Nº Axle load (ton) Axle load (kN) Multiple units (MU)/Locomotives:

MU series 3400 (4 units) 117.8 ton (30.9/43.1) 10 14.87/16 ton 133.5 kN MU series 4000 (6 units) 298.3 ton (25 ton) 24 14.40 ton 143.5 kN

MU series 592 (3 units) 130.4 ton 13.60 ton 135.5 kN

Locomotive series 5600 87 ton 4 21.75 ton 216.7 kN

Locomotive series 4700 86 ton 4 21.50 ton 214.2 kN

Locomotive series 1960 121 ton 20.15 ton 200.8 kN

Locomotive series 6000 125 ton 6 20.50 ton 204.3 kN

Freight wagons (tare+max.load):

series Ealos (33.8+56.3) ton 4 22.50 ton 224.2 kN

series Falls (24.4+65.6) ton 4 22.50 ton 224.2 kN

series Kbs (14.2+25.8) ton 2 21.00 ton 209.2 kN

series Sgnss (21.6+68.4) ton 4 22.50 ton 224.2 kN

Overview on railway stone masonry bridges

a) b)

Figure 2.11 – Trains nowadays in the Portuguese railway networks: a) Diesel locomotive series 6000 and b) MU series 4000.

According to UIC code 700 (UIC, 2004), the railway lines were classified, which can then be used to determine whether or not wagons shall be accepted on these lines as well as to determine the load limits, based on their geometrical characteristics in terms of axle distances, mass per axle and mass per unit length.

Railway infrastructure companies shall classify their lines or sections of line into line categories A, B1, B2, C2, C3, C4, D2, D3, D4, E4 and E5. To determine the line category, the railway companies shall take into account a train made up of an unlimited number of load models (design wagons). When assigning a line category to a section of a line, the railway infrastructure company must take into account the load-carrying capacity of the infrastructure (track, bridges, embankments, other civil engineering structures supporting the track, etc.) and their condition. The load models of UIC code 700 are only used for the classification of existing lines and should not be used for designing new railway infrastructures.

For that purpose, Eurocode 1 part 2 (CEN, 2003) for railway actions, should be used.

In Portugal, the railway infrastructure company, IP, classified the Portuguese rail lines according to UIC code 700 categories, presented in Table 2.4. The maximum category found is D4 and the lower category found is A. More than 80% of the Portuguese railways are in the D4 category, allowing the maximum load permitted in the Portuguese railway lines.

Table 2.4 – Railway line categories (IP).

Classification Wheelset load

Uniform vehicle load in ton/m

A B C D

16 tonnes 18 tonnes 20 tonnes 22.5 tonnes

5.0 A B1

6.4 B2 C2 D2

7.2 C3 D3

8.0 C4 D4

The new European Standard, EN 15528 (EN, 2013), introduced some modifications for the classification of railway lines and enforces all infrastructure managers to revise their line categories to these new provisions. According to this standard, when classifying the rail track into a category to be determined, the load capacity of the structures supporting the track shall be determined using load models of type vehicles and having the speed and type of traffic taken into account. In this standard, 18 different categories are defined, thus more than those defined by the UIC 700 code. Currently, to the best

knowledge of the author, the Portuguese infrastructure company, IP, has not yet adjusted the categories of rail tracks to the provisions of this new European standard.